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2019-02-03T02:20:00.000+05:30

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1. What is normalization? Explain different levels of normalization?

Check out the article Q100139 from Microsoft knowledge base and of

course, there's much more information available in the net. It'll be a

good idea to get a hold of any RDBMS fundamentals text book,

especially the one by C. J. Date. Most of the times, it will be okay

if you can explain till third normal form.

2. What is denormalization and when would you go for it?

As the name indicates, denormalization is the reverse process of

normalization. It's the controlled introduction of redundancy in to

the database design. It helps improve the query performance as the

number of joins could be reduced.

3. How do you implement one-to-one, one-to-many and many-to-many

relationships while designing tables?

One-to-One relationship can be implemented as a single table and

rarely as two tables with primary and foreign key relationships.

One-to-Many relationships are implemented by splitting the data into

two tables with primary key and foreign key relationships.

Many-to-Many relationships are implemented using a junction table with

the keys from both the tables forming the composite primary key of the

junction table.

It will be a good idea to read up a database designing fundamentals

text book.

4. What's the difference between a primary key and a unique key?

Both primary key and unique enforce uniqueness of the column on which

they are defined. But by default primary key creates a clustered index

on the column, where are unique creates a nonclustered index by

default. Another major difference is that, primary key doesn't allow

NULLs, but unique key allows one NULL only.

5. What are user defined datatypes and when you should go for them?

User defined datatypes let you extend the base SQL Server datatypes by

providing a descriptive name, and format to the database. Take for

example, in your database, there is a column called Flight_Num which

appears in many tables. In all these tables it should be varchar(8).

In this case you could create a user defined datatype called

Flight_num_type of varchar(8) and use it across all your tables.

See sp_addtype, sp_droptype in books online.

5. What is bit datatype and what's the information that can be stored

inside a bit column?

Bit datatype is used to store boolean information like 1 or 0 (true or

false). Untill SQL Server 6.5 bit datatype could hold either a 1 or 0

and there was no support for NULL. But from SQL Server 7.0 onwards,

bit datatype can represent a third state, which is NULL.

6. Define candidate key, alternate key, composite key.

A candidate key is one that can identify each row of a table uniquely.

Generally a candidate key becomes the primary key of the table. If the

table has more than one candidate key, one of them will become the

primary key, and the rest are called alternate keys.

A key formed by combining at least two or more columns is called

composite key.

7. What are defaults? Is there a column to which a default can't be bound?

A default is a value that will be used by a column, if no value is

supplied to that column while inserting data. IDENTITY columns and

timestamp columns can't have defaults bound to them. See CREATE

DEFUALT in books online.

SQL Server architecture (top)

8. What is a transaction and what are ACID properties?

A transaction is a logical unit of work in which, all the steps must

be performed or none. ACID stands for Atomicity, Consistency,

Isolation, Durability. These are the properties of a transaction. For

more information and explanation of these properties, see SQL Server

books online or any RDBMS fundamentals text book.

Explain different isolation levels

An isolation level determines the degree of isolation of data between

concurrent transactions. The default SQL Server isolation level is

Read Committed. Here are the other isolation levels (in the ascending

order of isolation): Read Uncommitted, Read Committed, Repeatable

Read, Serializable. See SQL Server books online for an explanation of

the isolation levels. Be sure to read about SET TRANSACTION ISOLATION

LEVEL, which lets you customize the isolation level at the connection

level.

CREATE INDEX myIndex ON myTable(myColumn)

9. What type of Index will get created after executing the above statement?

Non-clustered index. Important thing to note: By default a clustered

index gets created on the primary key, unless specified otherwise.

What's the maximum size of a row?

8060 bytes. Don't be surprised with questions like 'what is the

maximum number of columns per table'. Check out SQL Server books

online for the page titled: "Maximum Capacity Specifications".

10. Explain Active/Active and Active/Passive cluster configurations

Hopefully you have experience setting up cluster servers. But if you

don't, at least be familiar with the way clustering works and the two

clusterning configurations Active/Active and Active/Passive. SQL

Server books online has enough information on this topic and there is

a good white paper available on Microsoft site.

11. Explain the architecture of SQL Server

This is a very important question and you better be able to answer it

if consider yourself a DBA. SQL Server books online is the best place

to read about SQL Server architecture. Read up the chapter dedicated

to SQL Server Architecture.

12. What is lock escalation?

Lock escalation is the process of converting a lot of low level locks

(like row locks, page locks) into higher level locks (like table

locks). Every lock is a memory structure too many locks would mean,

more memory being occupied by locks. To prevent this from happening,

SQL Server escalates the many fine-grain locks to fewer coarse-grain

locks. Lock escalation threshold was definable in SQL Server 6.5, but

from SQL Server 7.0 onwards it's dynamically managed by SQL Server.

13. What's the difference between DELETE TABLE and TRUNCATE TABLE commands?

DELETE TABLE is a logged operation, so the deletion of each row gets

logged in the transaction log, which makes it slow. TRUNCATE TABLE

also deletes all the rows in a table, but it won't log the deletion of

each row, instead it logs the deallocation of the data pages of the

table, which makes it faster. Of course, TRUNCATE TABLE can be rolled

back.

14. Explain the storage models of OLAP

Check out MOLAP, ROLAP and HOLAP in SQL Server books online for more

infomation.

15. What are the new features introduced in SQL Server 2000 (or the latest

release of SQL Server at the time of your interview)? What changed

between the previous version of SQL Server and the current version?

This question is generally asked to see how current is your knowledge.

Generally there is a section in the beginning of the books online

titled "What's New", which has all such information. Of course,

reading just that is not enough, you should have tried those things to

better answer the questions. Also check out the section titled

"Backward Compatibility" in books online which talks about the changes

that have taken place in the new version.

16. What are constraints? Explain different types of constraints.

Constraints enable the RDBMS enforce the integrity of the database

automatically, without needing you to create triggers, rule or defaults.

Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY

For an explanation of these constraints see books online for the pages

titled: "Constraints" and "CREATE TABLE", "ALTER TABLE"

17. Whar is an index? What are the types of indexes? How many clustered

indexes can be created on a table? I create a separate index on each

column of a table. what are the advantages and disadvantages of this

approach?

Indexes in SQL Server are similar to the indexes in books. They help

SQL Server retrieve the data quicker.

Indexes are of two types. Clustered indexes and non-clustered indexes.

When you craete a clustered index on a table, all the rows in the

table are stored in the order of the clustered index key. So, there

can be only one clustered index per table. Non-clustered indexes have

their own storage separate from the table data storage. Non-clustered

indexes are stored as B-tree structures (so do clustered indexes),

with the leaf level nodes having the index key and it's row locater.

The row located could be the RID or the Clustered index key, depending

up on the absence or presence of clustered index on the table.

If you create an index on each column of a table, it improves the

query performance, as the query optimizer can choose from all the

existing indexes to come up with an efficient execution plan. At the

same t ime, data modification operations (such as INSERT, UPDATE,

DELETE) will become slow, as every time data changes in the table, all

the indexes need to be updated. Another disadvantage is that, indexes

need disk space, the more indexes you have, more disk space is used.

Database administration (top)

18. What is RAID and what are different types of RAID configurations?

RAID stands for Redundant Array of Inexpensive Disks, used to provide

fault tolerance to database servers. There are six RAID levels 0

through 5 offering different levels of performance, fault tolerance.

MSDN has some information about RAID levels and for detailed

information, check out the RAID advisory board's homepage

19. What are the steps you will take to improve performance of a poor

performing query?

This is a very open ended question and there could be a lot of reasons

behind the poor performance of a query. But some general issues that

you could talk about would be: No indexes, table scans, missing or out

of date statistics, blocking, excess recompilations of stored

procedures, procedures and triggers without SET NOCOUNT ON, poorly

written query with unnecessarily complicated joins, too much

normalization, excess usage of cursors and temporary tables.

Some of the tools/ways that help you troubleshooting performance

problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET

STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance

monitor, Graphical execution plan in Query Analyzer.

Download the white paper on performance tuning SQL Server from

Microsoft web site. Don't forget to check out sql-server-performance.com

20. What are the steps you will take, if you are tasked with securing an

SQL Server?

Again this is another open ended question. Here are some things you

could talk about: Preferring NT authentication, using server, databse

and application roles to control access to the data, securing the

physical database files using NTFS permissions, using an unguessable

SA password, restricting physical access to the SQL Server, renaming

the Administrator account on the SQL Server computer, disabling the

Guest account, enabling auditing, using multiprotocol encryption,

setting up SSL, setting up firewalls, isolating SQL Server from the

web server etc.

Read the white paper on SQL Server security from Microsoft website.

Also check out My SQL Server security best practices

21. What is a deadlock and what is a live lock? How will you go about

resolving deadlocks?

Deadlock is a situation when two processes, each having a lock on one

piece of data, attempt to acquire a lock on the other's piece. Each

process would wait indefinitely for the other to release the lock,

unless one of the user processes is terminated. SQL Server detects

deadlocks and terminates one user's process.

A livelock is one, where a request for an exclusive lock is

repeatedly denied because a series of overlapping shared locks keeps

interfering. SQL Server detects the situation after four denials and

refuses further shared locks. A livelock also occurs when read

transactions monopolize a table or page, forcing a write transaction

to wait indefinitely.

Check out SET DEADLOCK_PRIORITY and "Minimizing Deadlocks" in SQL

Server books online. Also check out the article Q169960 from Microsoft

knowledge base.

22. What is blocking and how would you troubleshoot it?

Blocking happens when one connection from an application holds a lock

and a second connection requires a conflicting lock type. This forces

the second connection to wait, blocked on the first.

Read up the following topics in SQL Server books online: Understanding

and avoiding blocking, Coding efficient transactions.

23. Explain CREATE DATABASE syntax

Many of us are used to craeting databases from the Enterprise Manager

or by just issuing the command: CREATE DATABAE MyDB. But what if you

have to create a database with two filegroups, one on drive C and the

other on drive D with log on drive E with an initial size of 600 MB

and with a growth factor of 15%? That's why being a DBA you should be

familiar with the CREATE DATABASE syntax. Check out SQL Server books

online for more information.

24. How to restart SQL Server in single user mode? How to start SQL Server

in minimal configuration mode?

SQL Server can be started from command line, using the SQLSERVR.EXE.

This EXE has some very important parameters with which a DBA should be

familiar with. -m is used for starting SQL Server in single user mode

and -f is used to start the SQL Server in minimal confuguration mode.

Check out SQL Server books online for more parameters and their

explanations.

25. As a part of your job, what are the DBCC commands that you commonly

use for database maintenance?

DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC,

DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc. But there

are a whole load of DBCC commands which are very useful for DBAs.

Check out SQL Server books online for more information.

26. What are statistics, under what circumstances they go out of date, how

do you update them?

Statistics determine the selectivity of the indexes. If an indexed

column has unique values then the selectivity of that index is more,

as opposed to an index with non-unique values. Query optimizer uses

these indexes in determining whether to choose an index or not while

executing a query.

Some situations under which you should update statistics:

1) If there is significant change in the key values in the index

2) If a large amount of data in an indexed column has been added,

changed, or removed (that is, if the distribution of key values has

changed), or the table has been truncated using the TRUNCATE TABLE

statement and then repopulated

3) Database is upgraded from a previous version

Look up SQL Server books online for the following commands: UPDATE

STATISTICS, STATS_DATE, DBCC SHOW_STATISTICS, CREATE STATISTICS, DROP

STATISTICS, sp_autostats, sp_createstats, sp_updatestats

27. What are the different ways of moving data/databases between servers

and databases in SQL Server?

There are lots of options available, you have to choose your option

depending upon your requirements. Some of the options you have are:

BACKUP/RESTORE, dettaching and attaching databases, replication, DTS,

BCP, logshipping, INSERT...SELECT, SELECT...INTO, creating INSERT

scripts to generate data.

28. Explian different types of BACKUPs avaialabe in SQL Server? Given a

particular scenario, how would you go about choosing a backup plan?

Types of backups you can create in SQL Sever 7.0+ are Full database

backup, differential database backup, transaction log backup,

filegroup backup. Check out the BACKUP and RESTORE commands in SQL

Server books online. Be prepared to write the commands in your

interview. Books online also has information on detailed

backup/restore architecture and when one should go for a particular

kind of backup.

29. What is database replicaion? What are the different types of

replication you can set up in SQL Server?

Replication is the process of copying/moving data between databases on

the same or different servers. SQL Server supports the following types

of replication scenarios:

* Snapshot replication

* Transactional replication (with immediate updating subscribers,

with queued updating subscribers)

* Merge replication

See SQL Server books online for indepth coverage on replication. Be

prepared to explain how different replication agents function, what

are the main system tables used in replication etc.

30. How to determine the service pack currently installed on SQL Server?

The global variable @@Version stores the build number of the

sqlservr.exe, which is used to determine the service pack installed.

To know more about this process visit SQL Server service packs and

versions.

Database programming (top)

31. What are cursors? Explain different types of cursors. What are the

disadvantages of cursors? How can you avoid cursors?

Cursors allow row-by-row prcessing of the resultsets.

Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See

books online for more information.

Disadvantages of cursors: Each time you fetch a row from the cursor,

it results in a network roundtrip, where as a normal SELECT query

makes only one rowundtrip, however large the resultset is. Cursors are

also costly because they require more resources and temporary storage

(results in more IO operations). Furthere, there are restrictions on

the SELECT statements that can be used with some types of cursors.

Most of the times, set based operations can be used instead of

cursors. Here is an example:

If you have to give a flat hike to your employees using the following

criteria:

Salary between 30000 and 40000 -- 5000 hike

Salary between 40000 and 55000 -- 7000 hike

Salary between 55000 and 65000 -- 9000 hike

In this situation many developers tend to use a cursor, determine each

employee's salary and update his salary according to the above

formula. But the same can be achieved by multiple update statements or

can be combined in a single UPDATE statement as shown below:

UPDATE tbl_emp SET salary =

CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000

WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000

WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000

END

Another situation in which developers tend to use cursors: You need to

call a stored procedure when a column in a particular row meets

certain condition. You don't have to use cursors for this. This can be

achieved using WHILE loop, as long as there is a unique key to

identify each row. For examples of using WHILE loop for row by row

processing

Write down the general syntax for a SELECT statements covering all the

options.

Here's the basic syntax: (Also checkout SELECT in books online for

advanced syntax).

SELECT select_list

[INTO new_table_]

FROM table_source

[WHERE search_condition]

[GROUP BY group_by__expression]

[HAVING search_condition]

[ORDER BY order__expression [ASC | DESC] ]

32. What is a join and explain different types of joins.

Joins are used in queries to explain how different tables are related.

Joins also let you select data from a table depending upon data from

another table.

Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs.
OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL

OUTER JOINS.

33. Can you have a nested transaction?

Yes, very much. Check out BEGIN TRAN, COMMIT, ROLLBACK, SAVE TRAN and

@@TRANCOUNT

34. What is an extended stored procedure? Can you instantiate a COM object

by using T-SQL?

An extended stored procedure is a function within a DLL (written in a

programming language like C, C++ using Open Data Services (ODS) API)

that can be called from T-SQL, just the way we call normal stored

procedures using the EXEC statement. See books online to learn how to

create extended stored procedures and how to add them to SQL Server.

Yes, you can instantiate a COM (written in languages like VB, VC++)

object from T-SQL by using sp_OACreate stored procedure. Also see

books online for sp_OAMethod, sp_OAGetProperty, sp_OASetProperty,

sp_OADestroy. For an example of creating a COM object in VB and

calling it from T-SQL, see 'My code library' section of this site.

35. What is the system function to get the current user's user id?

USER_ID(). Also check out other system functions like USER_NAME(),

SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().

36. What are triggers? How many triggers you can have on a table? How to

invoke a trigger on demand?

Triggers are special kind of stored procedures that get executed

automatically when an INSERT, UPDATE or DELETE operation takes place

on a table.

In SQL Server 6.5 you could define only 3 triggers per table, one for

INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0

onwards, this restriction is gone, and you could create multiple

triggers per each action. But in 7.0 there's no way to control the

order in which the triggers fire. In SQL Server 2000 you could specify

which trigger fires first or fires last using sp_settriggerorder

Triggers can't be invoked on demand. They get triggered only when an

associated action (INSERT, UPDATE, DELETE) happens on the table on

which they are defined.

Triggers are generally used to implement business rules, auditing.

Triggers can also be used to extend the referential integrity checks,

but wherever possible, use constraints for this purpose, instead of

triggers, as constraints are much faster.

Till SQL Server 7.0, triggers fire only after the data modification

operation happens. So in a way, they are called post triggers. But in

SQL Server 2000 you could create pre triggers also. Search SQL Server

2000 books online for INSTEAD OF triggers.

Also check out books online for 'inserted table', 'deleted table' and

COLUMNS_UPDATED()

37. There is a trigger defined for INSERT operations on a table, in an

OLTP system. The trigger is written to instantiate a COM object and

pass the newly insterted rows to it for some custom processing. What

do you think of this implementation? Can this be implemented better?

Instantiating COM objects is a time consuming process and since you

are doing it from within a trigger, it slows down the data insertion

process. Same is the case with sending emails from triggers. This

scenario can be better implemented by logging all the necessary data

into a separate table, and have a job which periodically checks this

table and does the needful.

38. What is a self join? Explain it with an example.

Self join is just like any other join, except that two instances of

the same table will be joined in the query. Here is an example:

Employees table which contains rows for normal employees as well as

managers. So, to find out the managers of all the employees, you need

a self join.

CREATE TABLE emp

(

empid int,

mgrid int,

empname char(10)

)

INSERT emp SELECT 1,2,'Vyas'

INSERT emp SELECT 2,3,'Mohan'

INSERT emp SELECT 3,NULL,'Shobha'

INSERT emp SELECT 4,2,'Shridhar'

INSERT emp SELECT 5,2,'Sourabh'

SELECT t1.empname [Employee], t2.empname [Manager]

FROM emp t1, emp t2

WHERE t1.mgrid = t2.empid

Here's an advanced query using a LEFT OUTER JOIN that even returns the

employees without managers (super bosses)

SELECT t1.empname [Employee], COALESCE(t2.empname, 'No manager') [Manager]

FROM emp t1

LEFT OUTER JOIN

emp t2

t1.mgrid = t2.empid
39. What is the difference between Function and Stored Procedure.

Stored Procedure (SP)	Function (UDF - User Defined Function)
SP can return zero, single or multiple values.	Function must return a single value (which may be a scalar or a table).
We can use transaction in SP.	We can't use transaction in UDF.
SP can have input/output parameter.	Only input parameter.
We can call function from SP.	We can't call SP from function.
We can't use SP in SELECT/ WHERE/ HAVING statement.	We can use UDF in SELECT/ WHERE/ HAVING statement.
We can use exception handling using Try-Catch block in SP.	We can't use Try-Catch block in UDF.

40. What is the difference between Trigger and Stored Procedure.

	1. We can execute a stored procedure whenever we want with the help of the exec command, but a trigger can only be executed whenever an event (insert, delete, and update) is fired on the table on which the trigger is defined.
	2. We can call a stored procedure from inside another stored procedure but we can't directly call another trigger within a trigger. We can only achieve nesting of triggers in which the action (insert, delete, and update) defined within a trigger can initiate execution of another trigger defined on the same table or a different table.
	3. Stored procedures can be scheduled through a job to execute on a predefined time, but we can't schedule a trigger.
	4. Stored procedure can take input parameters, but we can't pass parameters as input to a trigger.
	5. Stored procedures can return values but a trigger cannot return a value.
	6. We can use Print commands inside a stored procedure for debugging purposes but we can't use print commands inside a trigger.
	7. We can use transaction statements like begin transaction, commit transaction, and rollback inside a stored procedure but we can't use transaction statements inside a trigger.
	8. We can call a stored procedure from the front end (.asp files, .aspx files, .ascx files, etc.) but we can't call a trigger from these files.
	9. Stored procedures are used for performing tasks. Stored procedures are normally used for performing user specified tasks. They can have parameters and return multiple results set.
	10. The Triggers for auditing work: Triggers normally are used for auditing work. They can be used to trace the activities of table events.

PowerBuilder frequently asked questions by top companies

2019-02-02T20:45:00.000+05:30

PowerBuilder frequently asked questions by top companies

Question 1

What is the difference between SetTrans() and SetTransObject()?

Answer

In simple terms, SetTrans() gives you no control on the transactions. It automatically connects to and disconnects from the database after each Retrieve() and Update() function. It is useful when the number of connections are limited, but, you can't use this for multi-table update. On the other hand SetTransObject() gives you full control over the transactions. It is your responsibility to connect to and disconnect from the database and also, you need to issue COMMIT/ROLLBACK statements. This method is more efficient since there is no connect/disconnect overhead for each database operation.

Question 2

List all the buffers that a DataWindow control maintains.

Answer

Primary!, Delete!, Filter!, Original!, and one buffer for the edit control.

Question 3

When the DataWindow is set to ReadOnly, What buffers PowerBuilder maintains for the DataWindow Control?

Answer

PowerBuilder maintains all the four buffers, i.e., Primary!, Delete!, Filter!, Original!.

Question 4

How do you change the SQL Statement of a DataWindow at run-time?

Answer

You can either use the Modify() or .Object notation to change the SQL statement of a DataWindow control. In the SQLPreview event, you can change it using SetSQLPreview(). Outside SQLPreview event, you can call SetSQLSelect().

Question 5

The new .Object notation syntax for the DataWindow control replaces the Modify() function. Explain.

Answer

No, it doesn't completely replace Modify() function. You can create objects such as rectangle, text objects in the DataWindow object using the CREATE statement in the Modify() function. This can't be done with the .Object notation. It is also not possible to refer to the data by column name dynamically, which can be done using Modify().

Question 6

Describe where you can't use .Object notation for a DataWindow control instead of the Modify()?

Answer

You can't create objects in the DataWindow object dynamically using the .Object notation.

Question 7

How do you change the DataWindow object of a DataWindow control at run-time?

Answer

DataWindow_Control_Name.DataObject = 'New_DataWindow_Object_Name'

Question 8

What will happen if you pass extra retrieve arguments to the Retrieve() function for the DataWindow control?

Answer

PowerBuilder ignores extra arguments.

Question 9

What will happen if you pass no arguments to the DataWindow's Retrieve() function, when the DataWindow is expecting some arguments?

Answer

PowerBuilder prompts you for the arguments at run-time.

Question 10

Can you use an array as an argument to the DataWindow's Retrieve() function? If yes, How and where it is useful?

Answer

Yes, you can use PowerBuilder array as an argument to the Retrieve() function. This is useful when you use IN clause in the SELECT statement of the DataWindow's source.

Question 11

What would be the row status in the destination DataWindow when a row is copied from another DataWindow using RowsCopy() function?

Answer

NewModified!

Question 12

What would be the row status in the destination DataWindow when a row is copied from another DataWindow using RowsMove() function?

Answer

NewModified!

Question 13

I would like to allow the user to print selected rows. How it can be done?

Answer

Have a hidden DataWindow control or a DataStore and assign the same DataWindow object that you are using to display on the window. Copy selected rows to the DataStore or the hidden DataWindow control (You can use RowsCopy() function) and print the DataStore or the hidden DataWindow control.

Question 14

What are the different statuses a row in a DataWindow can have?

Answer

New!, NewModified!, DataModified!, NotModified!

Question 15

What are the different statuses a column in a DataWindow row can have?

Answer

DataModified!, NotModified!

Question 16

Explain the use of AcceptText() function.

Answer

This function applies the content of the edit control to the primary buffer after validating the data. PowerBuilder applies the edit control content to the Primary buffer whenever user press tab or click on another column within the DataWindow. if the user change the value of a single column and doesn't press either tab or click on another column, PowerBuilder will not copy the changed data, that means the changes will not be applied in the database. Calling the AcceptText() function solves this problem. You can also specify to the Update() via argument to call AcceptText() internally before applying the changes to the database.

Question 17

When you update the DataWindow, what would be the each row status in the DataWindow when the update is successful?

Answer

NotModified!

Question 18

You have deleted few rows, say 10 rows from a DataWindow, and update the DataWindow. How many rows would be available in the Deleted buffer after successful update?

Answer

Zero Rows.

Question 19

Explain the advantages and disadvantages of calling AcceptText() function from the ItemChanged event of a DataWindow control.

Answer

AcceptText() function shouldn't be called from ItemChanged event. This is because, AcceptText() function triggers the ItemChanged event. That means, calling AcceptText() in the ItemChanged event will go into a loop. So, there are only disadvantages, no advantages. If you really need to call AcceptText() from ItemChanged event, create a user-defined event and post that event from the ItemChanged event.

Question 20

How do you change the default DataWindow error message title?

Answer

Assign the application object's 'DataWindowMessageTitle' attribute with the new DataWindow error box title.

Question 21

Assume, you have marked a field as 'Required'. At run-time user tabs into that field and tabs out without entering a value in that field. Will PowerBuilder force the user for specifying a value? If not, how do you force the user for specifying the value?

Answer

As long as the user do not change (In this context, do not enter the data) the column's value, PowerBuilder do not force entering a value. The solution to this problem is, Call FindRequired() function before you update the DataWindow.

Question 22

Explain the DataWindow validation.

Answer

PowerBuilder checks whether the data is changed or not by comparing the edit control value with primary buffer. It checks for the data type correctness, if the data is changed. Wrong data type will trigger ItemError event. When the data passes the data type checking, it executes the validation rule. Invalid data will trigger ItemError event. Correct data will trigger ItemChanged event. If the ItemChanged event returns zero, it will trigger ItemFocusChanged event, otherwise ItemError will be triggered. Depending on the ItemError event's return value, either the cursor remains in the same column or will go to the next higher tab sequence's field (In this case, ItemFocusChanged event will be triggered).

Question 23

When two DataWindow are being shared, what exactly would be shared and are there any restrictions?

Answer

The presentation is not shared. The data (buffers including Delete! and Filter!) and the sort criteria is shared. There are few restrictions, which include, Crosstab DataWindow windows can't share data, the client and the server in the distributed computing mechanism can't share data. you can turn on the query mode only for the primary DataWindow. If a DataWindow is sharing data with a nested DataWindow, the handle to the nested DataWindow becomes invalid with each retrieval. So, GetChild() and ShareData() need to be called each time a nested DataWindow is retrieved.

Question 24

What is difference between 'prompt for criteria' and 'Query Mode'?

Answer

'Prompt For Criteria' as the name says, prompts for the criteria--for all those columns that were marked--in its own display dialog box and ignores the DataWindow you have painted. It also ignores the tab sequence number, i.e., prompts even if the tab sequence is zero. 'QueryMode' is more flexible than the 'Prompt for Criteria', and it uses the DataWindow you have painted. It allows querying on all non-zero tab sequence columns in the DataWindow and you do not mark any column for this purpose. The former one promts for the values every time Retrieve() is called, where as the later one takes values only when you turn it on--by enabling QUERYMODE property.

Question 25

Say, you have a DataWindow which returns 10,000 rows. After retrieving few rows, say, 100 rows, you have decided not to retrieve the rest of the rows. Explain different methods of canceling the result set.

Answer

There are two ways to accomplish this. In the first method, you can call DBCancel() to cancel the query from a CommandButton Clicked event or in other event. However, once PowerBuilder starts retrieving the data, it will not give the control to the user till it completes retrieval. So, you need to put some code/comments in RetrieveRow event which will yield a little bit.
In the second method, you can just return 1 from the RetrieveRow event.

Question 26

Say, you have a DataWindow with two fields, emp_name, emp_address. Now, the focus is on the emp_name field. When the user press tab, what would be the return value of GetColumnName() from A.) ItemChanged and B.) ItemFocusChanged events?

Answer

GetColumnName() returns 'emp_name' in the ItemChanged event and 'emp_address' in the ItemFocusChanged event.

Question 27

Explain the steps that are required to update a multiple-table DataWindow?

Answer

In short, using the Modify function or .Object notation, you need to make one table updatable. You also need to set the primary keys for that table. Then update the DataWindow with FALSE argument for the reset option in the Update() function. After successful update, make the second table updatable and the first one not-updatable. Now call Update() function with TRUE for the reset option (If there are more than two tables, use the TRUE option to the last table to be updated). Commit after successful update and Rollback on unsuccessful update.

Question 28

What you have to do if you want the PowerBuilder to prompt for the sort criteria at run-time?

Answer

Set the sort criteria to NULL value using the SetSort() function and call Sort() function.

Question 29

How many times PowerBuilder will retrieve data from the child DataWindow in the following situation. A DataWindow has a field with DDDW edit style. There are 1000 rows in the parent DataWindow.

Answer

It retrieves only once. The thumb rule here is that, PowerBuilder retrieves data from the child DataWindow only when the child DataWindow do not have data in it.

Question 30

What command/function you use to select a row?

Answer

SelectRow() function.

Question 31

If there are 10 rows selected in a DataWindow, and if you call DeleteRow() function, how many rows will be deleted? Explain.

Answer

DeleteRow() has nothing to do with the row selection. It deletes only one row that you specify as the argument to it. If you want to delete all the selected rows, you need to call DeleteRow() in a loop for each selected row (You can find the selected row by calling GetSelectedRow() function).

Question 32

You have defined a composite DataWindow 'd_master' which has two DataWindows 'd_emp_info', 'd_emp_paychecks'. 'd_emp_info' takes one argument and 'd_emp_paychecks' takes two arguments. 'd_master' is placed in 'DataWindow_1' DataWindow control. DataWindow_1.Retrieve( Arg1, Arg2, Arg3 ) will retrieve data without prompting. Do you agree? Explain.

Answer

PowerBuilder prompts for the retrieval arguments. This is because, you can't specify retrieval arguments in the Retrieve() function for the nested DataWindows. Instead, you need to set Nested_Arguments attribute using the Modify() function or .Object notation.

Question 33

What will happen when you pass a wrong argument to the Modify() function?

Answer

Returns the error code, but doesn't trigger any event such as DataWindow dbError or Error. However, doing the same using .OBJECT notation will generate error and trigger DataWindow Error event.

Question 34

What will happen when you use a wrong expression for a DataWindow in the .Object notation?

Answer

Will trigger Error event of the DataWindow control.

Question 35

What is the difference between 'Error' and 'dbError' events in a DataWindow control?

Answer

DbError event is fired when a database related error occurs. Error event at the DataWindow control level is triggered when a wrong expression is encountered in the .Object notation, or a OLE/OCX related error occurs. For database errors, if you do not write any code in DBError event, PowerBuilder displays the error in its own dialog box. In the later case, if you do not code to DataWindow ERROR event, it will fire Application SystemError event. If there is no code in that event, PowerBuilder displays the error message and terminates the application.

Question 36

Explain the following error: 'Row(s) changed between retrieve and update'. Also explain how you will get rid of that error?

Answer

PowerBuilder reports this error when some one/process updates the row after you retrieve it but before apply the changes. POWERBUILDER detects this type of error when you include the TimeStamp column in the DataWindow or use the 'Key columns and Updatable columns' in the WHERE criteria. We can't avoid this error. The solution to this problem would be, reselect the row that caused the error and display it to the user with appropriate message and then update the database again. You can use ReSelectRow() function to get the latest values for the error row.

Question 37

What is concurrency control? How do you control it from the PowerBuilder?

Answer

When multiple users are working on the same data, we have to make sure that we don't corrupt others changes, either by updating their changes without looking at them or by any other means. When we apply changes to the database, we have to make sure that no body changed the data between your read and update. This can be controlled (not exactly controlling, but, we can detect) using the appropriate WHERE clause option in the update properties in the DataWindow painter.

Question 38

Explain different ways of generating a serial number for a column in a table. Explain ways in PowerBuilder and in the database. Which method you recommend?

Answer

This has to be controlled from the database, not from the PowerBuilder. This is because, a unique serial number generated by a POWERBUILDER client may not be unique for other user or when it is put in the database. If the database supports auto incrementing (Different database vendors implement it in different ways, for ex: sybase implements using Identity column property, Watcom calls AutoIncrement, Oracle selects from a special table), then there is no problem. Otherwise, you can use a single row single column table to generate serial no. The method you choose might depend on the performance issues and number of expected inserts and other factors.

Question 39

I want to execute a stored procedure that is defined in the database, using the function call notation. What I need to do?

Answer

Define a function that refers to the stored procedure, in the transaction object and start using the function. It is something like declaring an external function, however, you can't declare a function for a stored procedure at any object other than a transaction object.

Question 40

Explain the steps involved in inserting your a layer between 'transaction' object and 'SQLCA'.

Answer

Create a standard class user object by inheriting from 'Transaction' object. Define the attributes and functions that you need. Now, ask the SQLCA to be of type YourTransactionObject instead of TRANSACTION object. This you can do in the application painter.

Question 41

Write the code to protect existing data from changes by the user in a DataWindow and allow adding new rows.

Answer

DataWindow_1.Object.Column1.Protect = '1~tIf(IsRowNew(),0,1)'

Question 42

Explain the method you follow when you want to skip printing all pages that are divisible by 7 (seven)?

Answer

Well, you can write code for the PrintPage event of a DataWindow control. Check whether the page number is divisible by seven, if so, then return 1.

Question 43

I want to use the value passed in the retrieval arguments in the DataWindow. What I need to do?

Answer

If you are using PowerBuilder version 4.0 or above, you should be able to see the retrieval arguments under in the 'Columns' listbox in the 'Expression' dialog box. So, you can use it as if it is a column.

Question 44

The following situation triggers 'SystemError' event at the application object. Explain. You are trying to update a table on which you don't have update privilege.

Answer

This will not trigger the SystemError event, since it is a database & DataWindow related error. It triggers DataWindow DbError event. If there is no script for that event, PowerBuilder displays the error message in the default way.

Question 45

You got 'Row(s) changed between retrieve and update' error. Now, you want to select the latest value of that changed row. How you do that?

Answer

Use ReSelectRow() function.

Question 46

In a DataWindow, there are few fields with validation rules, and few fields with script in the ItemChanged event. I want to display custom error message when data doesn't go through the ItemChanged event, but want to display default error messages when the data doesn't go through the validation rules. What should I do?

Answer

Well, define an instance variable. Turn it one when you decide the data is invalid in the ItemChanged event. In the ItemError event, return appropriate return code depending on the instance variable value and reset the instance variable to it's default value appropriately.

Question 47

I want to find out all the fields that doesn't have values and have 'Required' attribute turned on. What should I do?

Answer

Call FindRequired() function before you call Update() function.

Question 48

Can I store some data in the DataWindow? If yes, How?

Answer

Select Rows/Data from the menu when you are in the DataWindow painter design mode and add data to the DataWindow and save the DataWindow. The data now is stored as part of the DataWindow definition.

Question 49

What I need to do if I want the child DataWindow shouldn't retrieve the data automatically?

Answer

Store an empty row in the child DataWindow. PowerBuilder do not retrieve data from the child DataWindow since it sees data inside it. You can store data in the child DataWindow, by selecting Rows/Data from the menu when you are in the DataWindow painter design mode.

Question 50

How many DataWindow can share the data from a DataWindow?

Answer

There is no limitation on how many DataWindows can share data from the first primary DataWindow or from the secondary DataWindow that work as primary DataWindow for other DataWindows.

Question 51

What is the difference between a DataWindow and a DataStore object?

Answer

DataStore is nothing but a DataWindow without interaction related events and functions. DataStore has less overhead compared to DataWindow since the DataStore object do not have interaction related overhead. You can use DataStore as a parameter to a remote object function/event in the distributed computing and OLE automation, where as DataWindow can not be used in those situations.

Question 52

Can a DataWindow share the data from a DataStore?

Answer Yes.

Question 53

I have a table in which one column is of 'LongBinary' data type. Can I update this column using DataWindow? If yes, How?

Answer

A regular DataWindow do not support BLOB data types such as 'Long Binary', Sybase's Image & Text data type columns. You need to use 'DATABASE BLOB' object in the DataWindow object. You can update the database normally when you follow these steps.

Question 54

What is the difference between a 'Computed Column' and 'Computed Field'?

Answer

'Computed Column' is a column that you define as part of the SELECT statement. These values are calculated by the database and sent to the PowerBuilder client. 'Computed Field's' we define in the DataWindow bands and PowerBuilder calculates these values, not the database. Depending on your computing model 'Fat Client' or 'Thin Client' you can decide which one to use. If it is 'Fat Client' model, use 'Computed Fields', otherwise use 'Computed Columns'.

Question 55

Can you change the value of a 'Computed Field' at run-time?

Answer

No, you can't the Computed field value directly. However, you can change the column value that are part of the Computed field expression, by that Computed field value will be changed automatically.

Question 56

What is a Dynamic DataWindow and how do you create a Dynamic DataWindow?

Answer

Dynamic DataWindow is the DataWindow that is not painted at design-time, instead it is created at run-time. This is useful when you don't know the exact columns that you need to include in the DataWindow at design time. You need to use SyntaxFromSQL() function and Create() function to create a DataWindow dynamically.

Question 57

How can I search a DataWindow?

Answer

Use Find() function.

Question 58

In a DataWindow validation rule, how can I refer to the data that is entered by the user?

Answer

Call GetText() function in the validation rule to get the data entered by the user. If you want to paint the same in the Database painter, you can use @name where name can be any text. PowerBuilder automatically converts @name to GetText() in the DataWindow validation rule when you paint a DataWindow that uses that column.

Question 59

Explain how 'Retrieve Only Needed' works.

Answer

By default, PowerBuilder displays the first row on the screen when it completes retrieving all the result set. That means, if there is huge result set, user has to wait for long time to see the first row on the screen. If you turn on 'RetrieveOnlyAsNeeded' property, PowerBuilder retrieves only those rows that fit on one screen. That means, user will see the data quickly. When the user scrolls, PowerBuilder retrieves again (as many rows as required). This option might affect the database server performance also, since the result is queued at the database till PowerBuilder client completes retrieving.

Question 60

What should I do if I want to display rows as soon as they are retrieved from a DataWindow?

Answer

Write code in the RetrieveRow event, at least a single line comment. And also set the 'Async' attribute in the DbParm property of the transaction object.

Question 61

Say, you have a DataWindow 'd_emp' which has a field 'emp' with DDLB edit style. When you read the field value using GetItemxxxxxxxx() function, what value is returned, 'Display Value' or 'Data Value'? What you need to do to get other value?

Answer

Use the LookupDisplay() function.

Question 62

How do you handle variable length text fields in a DataWindow?

Answer

Set the 'AutoSizeHeight' property in the detail band of the DataWindow when you are in the DataWindow painter design mode.

Question 63

How to retrieve multiple result set of a stored procedure in a single DataWindow?

Answer

A DataWindow can retrieve only one result set at a time. If you want to retrieve other result sets also, you can change the result set number either by Modify() function or using .Object notation. When you change the result set, make sure the number of columns and data types match with the existing DataWindow definition.

Question 64

How to retrieve a particular result set of a stored procedure in a DataWindow?

Answer

You need to suffix the result set number to the stored procedure name separated by semicolon.

Question 65

How to load a text file in a DataWindow?

Answer

Well, you can use ImportFile() function.

Question 66

What is a CrossTab presentation Style DataWindow? What are the places you can use this type of DataWindow?

Answer

Crosstab presentation style DataWindow allows to shorten the length of the report and display the data in a two-dimensional spreadsheet like report. One dimension displays in columns and the other as rows.

Question 67

How do you update a 'Group' presentation style DataWindow?

Answer

A DataWindow with 'Group' presentation style can't be updated.

Question 68

How do you update a 'OLE' presentation style DataWindow?

Answer

OLE presentation style DataWindow is only for display, you can't update that DataWindow.

Question 69

What are code tables and how you can use them in a DataWindow?

Answer

Code tables are used for translation. Typical use of code table is to display long description about the data, say, 'New York' and store the abbreviation in the database, say, 'NY'. You can use code tables in the DataWindow for the EditMask edit style only.

Question 70

What is the difference between a 'column name' and 'database column name'. Can you change any of these at painting time? If yes, How?

Answer

'Column Name' is the name of the column in the DataWindow. You always refer to this name when you want to change the column attributes. You can change the column name in the DataWindow. The 'Database column name' is the name of the column in the database and you can't change this name. Typically, this name is prefixed with the database and table and owner name. You can see both column and database column names by selecting 'Rows/Columns' in the DataWindow when you are in the DataWindow design mode.

Question 71

You have a DataWindow that has 100 rows. I want to append the rows to the existing rows when I retrieve next time in that DataWindow. Explain the required steps to do this.

Answer

Return 2 in the RetrieveStart event of that DataWindow control.

Question 72

What is the event from which I can see the exact SQL statement that is being sent to the database by PowerBuilder?

Answer

SQLPreview event of the DataWindow control.

Question 73

How to refer to a DataWindow column by the column number in the 'Describe()' and 'Modify()' functions.

Answer

You need to prefix the column number with pound (#). For example, DataWindow_1.Modify( '#10.TabSequence=0' ) sets the column number ten's tab order to zero.

Question 74

How to update a DataWindow that has 'Stored Procedure' as the data source?

Answer

Go to the update properites of the DataWindow by selecting Rows/Update properties from the menu when you are in the design mode in the DataWindow painter. Type the table name to update in the 'Table' prompt. Make sure the column names and data types are same.

Question 75

What are the uses of a DataWindow with 'External' data source?

Answer

'External' DataWindows are useful when you want to use the power of DataWindows, even though you are not retrieving the data from the database. Some of the features which would be more difficult to implement without using a DataWindow are, sorting, filtering, printing, exporting data into different formats, print previewing/zooming and so on.

Question 76

How many 'OLE DATABASE' columns you can use in one DataWindow?

Answer

Well, you can paint as many OLE Database BLOBs as you wish in a DataWindow. However, the update is not going to take place when you place more than one OLE Database BLOB object in a DataWindow.

Question 77

What are different types of windows available in PowerBuilder?

Answer

There are six different types of windows available in PowerBuilder. Those are Main, Popup, Child, Response, MDI Frame, MDI Frame with Microhelp.

Question 78

If I create a response window and open that window in an MDI frame using OpenSheet(), what will happen?

Answer

When you open a window in a MDI frame using OpenSheet() or OpenSheetWithParm() functions, that window get the sheet properties, irrespective of the window type. That means, when you open the response window using one of those functions, the window will behave like any other sheet, i.e., gets maximize, minimize, close controls on the title bar.

Question 79

Explain how a popup window is different from a child window?

Answer

Popup window can go beyond the parent window borders and Popup window is always on the top. On the other hand, the Child window can't go beyond parent window borders. Child window is never considered as an Active window from the programming perceptive.

Question 80

What is MDI_1?

Answer

MDI_1 control represents the 'Client Area' in a 'MDI frame' or 'MDI frame with Microhelp'. That means, all the window area other than 'Titlebar', 'Menu', Microhelp statusbar' is MDI_1. When you paint any object in the MDI window, you need to resize the client area programmatically by referencing MDI_1, otherwise, MDI_1 control size is not determined. That means, we can't see any sheet that we open in the client area, unless we resize the MDI_1 control.

Question 81

What should I do if I want to paint a window control in a MDI Frame window?

Answer

You need to resize the MDI_1 control. Window's resize event is the good candidate to write the script for MDI_1 control re-sizing. You need to reduce the size of the MDI_1 control by the size of all the controls that you have placed in the window.

Question 82

Can I have multiple MDI frame windows in the same application?

Answer

Well, technically, you can have multiple MDI windows in the same application. You can call Open() function twice, one for each MDI window. Please note that, the user might think that, two applications are running, since two different windows will appear with different menus.

Question 83

I need to declare an Instance variable for a DataWindow control ONLY, in a window. What should I do?

Answer

When you declare an instance variable at a window, it is accessible to all controls in the window. First of all, you can't declare an Instance/Shared variable for a specific control in a window. If you have the need of that, you need to create a user object of that specific control and declare instance/shared variables in the user object. Then place the user object in the window. In summary, a window control can't have it's own instance/shared variables, but the user object can (in the user object painter ONLY, not in Window Painter).

Question 84

Can I have a global and local variable with the same name?

Answer

Yes, You can have global and local/instance variable with the same name.

Question 85

You have declared a global variable xyz and a local variable xyz in the clicked event of a CommandButton. When you refer to xyz in the CommandButton's clicked event, which variable is referred? Global or Local?

Answer

Well, when you refer to xyz variable, POWERBUILDER search for the variable in local, instance/shared, instance/shared at the ancestor, global order. That means, in this case, the local variable is referred. To refer to the global variable which has the same name of a local variable, you need to prefix double colon before the variable name.

Question 86

How a 'Shared Variable' is different from a 'Instance Variable'?

Answer

Well, the value of an instance variable in each instance is independent of other instances. Instance variables are created when the object is created and will be destroyed when the object is destroyed. On the other hand, the shared variable is shared between different instances of the variable. That means, changing the shared variable in one instance will affect other instances. The shared variable is created when the FIRST instance of the object is created and is destroyed when the application is closed. You can't refer to an object's shared variable when none of the instance is open, even though the shared variables exists in the memory.

Question 87

Tell me some situations where you need to use shared variables.

Answer

One typical situation would be, counting the number of instances of a sheet. Another situation will be, you can use the shared variable to prevent the user updating the same record from multiple instances of the same window with different values.

Question 88

When a function argument is declared 'By ReadOnly', what you can do on that variable and what you can't do?

Answer

You can refer to that argument, you can change the value of the argument. But, you can't assign another object to that object. For example, say, a DataWindow is passed as a 'By ReadOnly' argument. You can change the value of any column/row of that DataWindow, but you can't say: arg_DataWindow = Another_DataWindow. In this case, you are assigning another object to this object. That means, you are asking to change the pointer to refer to the new object instead of the original object, which is not allowed when the argument is passed by 'By ReadOnly'.

Question 89

What is the difference between passing a function argument 'By Value' and 'By Reference'?

Answer

When an argument is passed 'By Value', the changed value of the argument in the called function will not be available in the calling object. On the other hand, when the argument is passed 'By Reference', the changed value of the argument in the called object IS AVAILABLE in the calling object. In case of 'By Value', POWERBUILDER sends a copy of the object, where as a pointer is send when passed by 'By Reference'.

Question 90

Can you declare CONSTANTS in PowerBuilder?

Answer

From version 5.0 onwards, you can declare constants in POWERBUILDER. For example: CONSTANT APPEND_TO_ROWS 2. When you want to append to the existing rows in the DataWindow when you retrieve next time, write 'return APPEND_TO_ROWS' instead of 'return 2'. Using constants you can make the code more readable and also more efficient (in some places).

Question 91

Explain the use of ANY data type.

Answer

ANY data type was introduced in version 4.0. You can use this data type when you really not sure about the return value of function. For example, OLE 2.0 control and in OLE automation. You really don't know what object/error code will be returned by the OLE client. Sometimes, those are compatible with POWERBUILDER data types. In those cases, you can use this variable to store the return value and CAST it to another data type before you operate on the value.

Question 92

How do you declare a function that returns nothing?

Answer

Type '(None)' without quotations in the 'Return Value' prompt when you are in the function painter.

Question 93

How to execute the ancestor event's script from the descendant's event?

Answer

You can use CALL SUPER::EVENT_NAME syntax.

Question 94

What will happen when you TRIGGER a non-existing event?

Answer

If you trigger a non-existing event using the old syntax, TriggerEvent(), nothing happens. In the new syntax, you can't trigger a non-existing event unless you use DYNAMIC keyword. When you trigger the event dynamically, NULL value will be returned.

Question 95

What will happen when you TRIGGER an event that doesn't have any script?

Answer

Nothing will happen. You are not allowed to capture the return value of an event which returns nothing. NULL value is returned when you trigger an event which has no script.

Question 96

What is the difference between TriggerEvent() and PostEvent()?

Answer

TriggerEvent() executes the specified event's script right away. PostEvent() posts the requests in the operating system's queue. This doesn't mean the posted event's script will be executed after completing the current script execution. It might execute right away also, it depends on how many requests are in the Operations system's message queue.

Question 97

What is the difference between TriggerEvent() and Send()?

Answer

TriggerEvent() JUST executes the specified event's script, but, it do not really trigger the event. For example, triggering the window's 'Close' event will execute the script written for that event, but, will not close the window. If you use Send() function, it does both, i.e., executes the script and closes the window also.

Question 98

How PowerBuilder executes events? Bottom-to-Top or Top-to-Bottom?

Answer Top-to-Bottom

Question 99

In the inheritence hirerachy, How PowerBuilder search for a function? Top-to-Bottom or Bottom-to-Top?

Answer

Bottom-to-Top

Question 100

Explain different levels of attribute/method protection available in PowerBuilder?

Answer

Public, Protected, Private, PrivateRead, PrivateWrite, ProtectedRead, ProtectedWrite

Question 101

How do you pass a value to a window at opening time?

Answer

Use either OpenWithParm() or OpenSheetWithParm() function depending on whether you are trying to open a window as a window or a sheet.

Question 102

Explain what a 'Message' object is and How it is useful in the programming?

Answer

'Message' object contains the messages that are sent by the operating system and sent by the POWERBUILDER scripts. It always contains only one message, that is the latest one. When you use OpenWithParm(), OpenSheetWithParm(), OpenUserObjectWithParm(), those parameters are placed in the 'Message' object and you can access those parameters in the opening object from the 'Message' object. Changing the values of the 'Message' object affects the event execution. For example, changing the 'ReturnValue' of the Message object in the window's CloseQuery event to 1 will stop the window being closed.

Question 103

What is the difference between 'Close' and 'CloseQuery' event?

Answer

POWERBUILDER triggers 'CloseQuery' event before it triggers 'Close' event. If 'CloseQuery' event's script is not executed successfully (in terms of return value), 'Close' event will never trigger.

Question 104

Explain typical scripting that you do in the 'CloseQuery' event?

Answer

Typical scripting would be, checking for unsaved work and prompting the user for the same and take action depending on the user's response.

Question 105

What should I do if I want to use '-' (hyphen) in identifiers in PowerScript?

Answer

Add 'DashesInIdentifiers=1' without quotations to the [POWERBUILDER] section in the POWERBUILDER.INI file.

Question 106

Explain different debugging mechanisms in PowerBuilder.

Answer

First mechanism would be obviously the debug painter. You can also use TRACE flag to log all the ODBC calls, /PBDEBUG to log the POWERBUILDER script execution.

Question 107

What should I do if I want to call a Windows SDK API?

Answer

You need to declare the Windows SDK API as an external function either locally or globally depending on your need. Then only you can refer to that function in PowerScript. If you have the same function name in PowerScript also, you can alias the external function in the declaration.

Question 108

List three PowerBuilder pronouns that we use to reduce hard-coding.

Answer

THIS, PARENT, PARENTWINDOW

Question 109

How 'Parent' is different from 'ParentWindow'?

Answer

'Parent' pronoun is used to refer to the object in which the current object is. For example, referring to 'Parent' in a CommandButton's script will refer to the window in which the CommandButton is placed. This is used in window control's scripts and functions. On the other hand, 'ParentWindow' is used to refer to the window for which the current menu is attached.

Question 110

What should I do if I want to display an User Object at specific location in a window dynamically?

Answer

You can specify the X and Y co-ordinates in the OpenUserObject() and OpenUserObjectWithParm() functions.

Question 111

Did you ever use Handle()? Where and How?

Answer

Handle() function gives the handle number of a given window. In simple terms, it is the number that identifies a window uniquely. You can use this function to check whether a particular window is open or not. Especially useful when you want to check whether another instance of the same application is running or not. You can use this function along with FindWindow() Windows API call.

Question 112

I want to find out whether the PowerBuilder application is still connected to the database or not. What should I do in the PowerScript?

Answer

Use DbHandle() function.

Question 113

I have a window which has a menu associated with. For some reason, I deleted the menu. Now, I am getting error when I try to open the window. What should I do?

Answer

If you remember the menu name, just create a dummy menu with the previous menu name. Now you should be able to open the window. Then, you can de-reference the menu from the window. If you don't remember the menu name, export the window and look in the exported file for the menu name. If you know really, you can edit the exported file and import it back otherwise, just note down the menu name and follow the first method.

Question 114

There is a ancestor window 'w_1' with one SingleLineEdit control 'sle_1'. Now, I created another window 'w_2' by inheriting from the 'w_1' window. In 'w_2' I changed the window background color to Pink. Then, I went back to 'w_1' and changed the window background color to Blue and 'sle_1' background color to Red. What color changes will reflect in 'w-2' window?

Answer

The thumb rule is that, if you have done any changes to a specific attribute in the descendent, then any further changes to the same attribute in the ancestor WILL NOT affect in the descendent. That means, since you have changed the window background color in the descendent, ancestor's background color change do not affect the descendent. You haven't changed the background color for the sle_1 in the descendent, So, the background color change for the sle_1 in the ancestor will reflect in the descendent also.

Question 115

What are PowerBuilder system tables and how they are useful for a PowerBuilder programmer?

Answer

There are five POWERBUILDER system tables, 'PBCatCol', 'PBCatEdt', 'PBCatFmt', 'PBCattbl', 'PBCatVld'. These tables store all the table, column specific information and POWERBUILDER extended attributes. These tables are created in the connected database by POWERBUILDER when the first user connects for the first time. These tables allow you defining extended attributes such as validation rule, edit style, display style, etc.. Once you create the extended attributes, these values are by default used when you create a DataWindow, which will reduce a lot of work and makes dws more consistent.

Question 116

How do you synchronize Database tables with the PowerBuilder catalog?

Answer

In the database painter, there is an option to synchronize POWERBUILDER system tables with actual table/column information.

Question 117

What is a validation rule? How PowerBuilder validation rule is different from the Database (validation) rules?

Answer

Validation rule specifies valid values for a specific column. It allows you to specify different valid values depending on the content of other columns. Validation rules defined in POWERBUILDER are used only POWERBUILDER clients. If another application connects to the database from Excel or Delphi, the database is not going to validate the data, since, the validation rule is not defined in the database. Please note that, the validation is done by POWERBUILDER not by the connected database. On the other hand, if you define the validation rule in the database, database will validate the value irrespective of the client type. In this case the validation is done by the connected database not by PowerBuilder.

Question 118

Explain different ways of executing a database stored procedure from PowerBuilder.

Answer

You can source the stored procedure to a DataWindow. You can also execute in the embedded and dynamic SQL. With version 5.0, you can declare a function for the stored procedure in the transaction object and execute the stored procedure as if you are executing a function.

Question 119

What is a proxy object and what is a remote object?

Answer

Proxy object represents the remote object in the distributed computing. Whenever you create a custom class user object, you can specify the proxy name. POWERBUILDER automatically saves the proxy object whenever you save user object. You place the actual user object in the server application and keep the proxy object in the client application. Before you act on the proxy object, you need to call SetConnect() function to connect to the server object.

Question 120

What is DDE?

Answer

DDE means Dynamic Data Exchange. This technology allows two different applications talk to each other under MS-Windows environment and exchange data between them.

Question 121

List few DDE related events.

Answer

'HotLinkAlarm', 'RemoteExec', 'RemoteHotlinkStart', 'RemoteHotlinkStop', 'RemoteRequest', 'RemoteSend'.

Question 122

What is the PowerBuilder object that has DDE related events?

Answer

Window

Question 123

What is difference between 'Cold Link' and 'Hot Link'?

Answer

In case of Hot link, the changed data is sent to the client automatically by the server. In case of 'Cold Link', the changed data is available to the DDE client only when it requests for that.

Question 124

What is the difference between 'In-Place editing' and 'Off-site editing'?

Answer

In case of 'Off-Site Editing', the OLE Server allows you editing in a separate window other than the OLE client application window. In case of 'In-Place Editing', the OLE server gets activated in the OLE Client application window and all the menu options will change accordingly. In this model, user feels that he is working in a single application even though he is using a different application.

Question 125

What is OCX control? Explain the required steps involved in CREATING an OCX control in PowerBuilder?

Answer

OCX is a OLE control which implements the component based architecture. You can use OCX control in any application that supports OLE 2.0. This increases the object reusability. You can use the OCX control in POWERBUILDER, but, you can't create a OCX control in POWERBUILDER in version 5.0.

Question 126

What is the difference between 'Embedding' and 'Linking' in the OLE context?

Answer

When you embed an object, the embedded object will be saved as part of the OLE container object. That means, any future changes to the actual object will not reflect in the embedded object. This also increases the storage requirement. Embedded object allows In-Place editing. In case of 'Linking', the original object resides where it was and a link information is stored in the OLE container object. That means, any future changes to the actual object will automatically reflect in the OLE container object. Linked objects are always invoked for editing off-site.

Question 127

What is 'AutoInstantiate' and where it is useful?

Answer

The user object that has 'AutoInstantiate' attribute turned on, will automatically creates an instance of that object whenever the object is declared. You need to use the CREATE statement to create the object after declaration when this property is not set. This attributes is available only for custom class user objects.

Question 128

What are the different places you can use OCX control in PowerBuilder?

Answer

You can use OCX control in a window, in a user object and in a DataWindow.

Question 129

Several times I heard 'Registry' in the technical meetings. What exactly 'Registry' is?

Answer

Registry is a MS-Windows database that contains information about each application. The application populates the information about it self using Windows API calls. Previously, application specific information such as application preferences, settings are stored in .INI file which is an ASCII file. Even though there was registry under MS-Windows 3.x, it wasn't really used by most of the applications and it was just used to store DDE and OLE specific information. The data is stored in the registry in the directory like hierarchy format.

Question 130

Explain the steps required to create a C++ user object in PowerBuilder?

Answer

Basically, you need to invoke the user object painter for C++ user object type. You need to declare any instance/shared variables and functions. While declaring functions, you just declare the function interface, not the function code. You need to write the actual code for functions in the C++ Editor which comes with POWERBUILDER. When you save the user object. POWERBUILDER automatically save the user object as a DLL and you need to deploy this DLL along with your application.

Question 131

We have migrated all our applications from Visual Basic to PowerBuilder. I would like to use those VBX controls, instead of re-coding in PowerBuilder. Is it possible? If Yes, are there any restrictions?

Answer

If you are using POWERBUILDER versions prior to 5.0, you can create a user object of type VBX and reuse your VBX control. The limitation is that, only Visual Basic v1.0 specific VBXes are supported by POWERBUILDER. In POWERBUILDER 5.0, you can't use VBX any more. Actually, it would be better stop using VBX and migrate to OCX which allows deploying your applications in 32-bit environment.

Question 132

The OCX control I planned to use has a 'Clicked' event. The OLE 2.0 control in PowerBuilder already has 'Clicked' event. What should I do?

Answer

When you are in the design mode, delete the duplicate events by selecting 'Declare/User Events' from the menu. This will solve the run-time problems.

PowerBuilder Interview Questions & Answers Section1

2009-11-28T20:49:00.000+05:30

1. Please tell me some thing about yourself?
My name is Umesh Kumar Yadav. I've completed GNIIT Three years certification course from NIIT Faridabad and also I've done MCA from M. D. University Rohtak.

About Work & Experience...

2. What is the difference between SetTrans() and SetTransObject()?
Define All process of material Generate indent to issue product.
3. How do you pass parameters when opening a window?

Use OpenWithParm method () and accessing the three system message object properties:
Message.DoubleParm
Message.PowerObjectParm
Message.StringParm
The parameters are stored in the Message object.

4. What are the different status’s a row can have in a DW and what function do you call to find the status?
The 4 DW Statuses:
1. Not Modified – the information in the row/column is unchanged from what was retrieved.
2. Data Modified – the information in a column or one of the columns in the row has changed since it was retrieved
3. New Modified – the row is new and values have been assigned to columns. (Changes are primarily due to user entry or by using the setitem () method)
4. New – the row is new and values have not been specified to columns.

a) All are applicable to rows but only 1 & 2 are applicable to columns.
b) Getitemstatus () can be used to find the data window status

5. What is the purpose of using the SUPER keyword?
It is used to refer to an object’s immediate ancestor. Take for example Super:: wf_myfunc (myarg1, myarg2). This example calls the ancestor function wf_myfunc (presumably the descendant also has a function called wf_myfunc). This example must be part of a script or function in the descendent window, not one of the window's controls

6. What is a dynamic data window? Give an example of why you’d need to use a dynamic data window.
It is a data window that is modified or created during runtime. CREATE method can be used to create or replace the current DW object in the DW control with the newly created DW. Settransobject () needs to be reset with the new DW in the control since the earlier association would have been destroyed.

7. What is the difference between ItemError () and DBError ()?
ItemError () occurs when the data supplied to a particular column in a table fails some validation rules. For example a DW column designed to accept only integer values throws this error if a string value is passed. DBError () occurs when INSERT/UPDATE/DELETE/RETRIEVE fails. When it occurs, the DW Control throws up a message box describing the error to the DBMS. The user can also get the appropriate error code and throw up message boxes.

8. What is a data store? What type of events does it support/not support?

It is a non-visual data window. For example if you want to retrieve data from a table without showing it, then you can go for data store. It does not support clicked events but supports deleterow (), insertrow (), retrieve () and update (). It also supports ItemError () event.

9. As an extension of (8) above, mention two differences with data windows
a) A DW can be designed such that the user is prompted to enter the parameters for data retrieval while this not possible with data store. If the user calls the RETRIEVE method for a DW control, the DW object expecting an argument, if the user leaves it blank, it prompts the user to enter an appropriate value, this behaviour is not supported in data stores
b) The PRINT Set-up dialog box for setting print specifications is not possible in data stores

10. Explain the following terms: Regeneration, Optimisation & PBD
a) Regeneration – when you modify an ancestor object, you can regenerate descendants so they pick up the code changes to the ancestor.
b) Optimisation – it is the process of compressing library objects; it removes gaps in libraries and defragments the storage of objects, thus improving performance. Optimising only affects the layout on disk and not the contents of the objects. Objects are not recompiled. For best performance libraries should be optimised once a week.
c) PBD – DW objects are stored in PBLs that are converted to PBDs thereby providing runtime versions of DW objects.

11. When do you use a data pipeline?
If the user wants to copy DB objects from one database to other or copy from one DBMS to another, the data pipeline can be used. The file can be exported from one database and imported to the target database. In the Data Pipeline painter you define a data source, source database, target database, retrieval arguments, unions, sorting, selection, and grouping criteria.

12. Explain and differentiate between settrans () and settransobject ()?
While using settrans () the user need not specify an explicit CONNECT or DISCONNECT statement in the script since PB internally calls them whenever required. As part of internal transaction management of DW controls, when the DW needs to access the DB, the DW control issues an internal CONNECT, performs data access and then issues an internal DISCONNECT.
Settransobject () is used when the user goes for a separate transaction object (example SQLCA) or creates a separate one in the script. The sequences of statements are as follows:
Transaction tra_1
tra_1 = CREATE transaction
tra_1.DBMS = “ODBC”
tra_1.database = “myDB”
CONNECT using tra_1
Dw_1. Settransobject (tra_1)
Dw_1. Retrieve ()

13. Explain the components of ODBC architecture
a) Application – any front end/GUI from where ODBC calls are made
b) Driver Manager – it is a DLL that controls loading of appropriate drivers to connect to DBMS. When an ODBC call is made, it scans the *.ini files to determine which driver to use
c) Driver – it is the heart of ODBC that takes care of N/W protocols to connect to the data source; it also submits SQL statements to the data source
d) RDBMS – an ASCII file containing information such as DBMS name, login/password etc

ODBC takes care of locating the Sybase/SQL server address on the network by reading the win.ini/sql.ini files

14. Explain the “Connect String DBParm” parameter in PowerBuilder.

It specifies the parameters required to connect to an ODBC data source. PowerBuilder uses these parameters to connect to the database. The syntax is
Connect String = 'DSN = data_source_name; {UID = user_Id; PWD = password; driver_specific_parameters}'
PowerBuilder generates the Connect String automatically when you define an ODBC data source and copies it to the DBParm box in the Database Profile Set-up dialog box. This happens before you connect to the data source in PowerBuilder.

15. Which are the PFC class libraries in PowerBuilder?
PFC is a combination of reusable and extendible classes and framework. The 8 libraries are:
a) pfcmain.pbl – basic services
b) pfcapsrv.pbl – application
c) pfcdwsrv.pbl – data window
d) pfcwnsrv.pbl – window
The 4 extension layer class libraries are pfemain.pbl, pfeapsrv.pbl, pfedwsrv.pbl & pfewnsrv.pbl. 2 more security related libraries (with no extension layers) are pfcsecad.pbl & pfcsecsc.pbl

16. When should internal transaction management be used?
It can be used if the number of connections to theDB are limited and also for pure retrieval when COMMIT & ROLLBACK are not application priorities.

17. Explain the different types of data sources that can be linked to data window controls
a) Quick Select – Used when data comes from one or more tables linked by a foreign key.
b) SQL Select – In addition to above grouping & computed columns can be specified
c) External – the data can be imported from a flat file or populated from the code. ( for example using setitem() methods)
d) Query – used when the data source (SQL statement) is saved in a query object defined in the query painter.
e) Stored Procedure

18. Explain how the Auto Commit property works in PB.

When the Auto Commit property is set to FALSE (default) or 0, PB issues SQL statements inside the scope of a transaction. 1(TRUE) implies statements outside the scope of a transaction (for example when your application requires creating temporary tables).
a) If you want to execute stored procedures containing DDL (CREATE, ALTER, DROP etc) statements, then Auto Commit = TRUE.
b) If Auto Commit = TRUE, then rollback cannot be issued, it should be set to FALSE after completing the DDL operation.
When Auto Commit is set from FALSE to TRUE, then PB issues a COMMIT statement by default.

19. Explain the steps to update a multi-table DW in PB.
The following steps are involved in the process:
a) Use. modify/.object notation to make ONE table updateable
b) SET the primary keys for the table
c) Perform DW_1 update with FALSE argument for the reset option in the Update() function
d) After © is successful, make 2nd table updateable and 1st table not updateable
e) Next call update() with TRUE argument for the the reset option in the Update() function
f) COMMIT/ROLLBACK depending on success or failure

20. What is a DWChild object? Name two events associated with it
A dropdown DW is aDWChild. For example a DW object that populates a column having the dropdown DW edit style is aDWChild object. It does not have any events associated with it.

21. Explain multi-byte support for PB
PB 8 supports both ANSI and double-byte character sets (DBCS); any PB8 application runs in a DBCS environment. In a DBCS environment 1 character = 2 bytes as opposed to 1 byte in an ANSI environment. For example we may need to change the width of a column of type char (40) to char (80).
The wide version of the Len () function (called Lenw ()) should be used since the former returns the number of bytes while the latter returns the number of characters.

PowerBuilder can access Unicode data in an ASE 12.5 Unicode database or in Unicode columns in ASE 12.5. PowerBuilder converts between double-byte character set (DBCS) data and Unicode automatically, provided that the Locale parameter is set with DBCS values. For example, the Locale DBParm should be set to chs or cht.

22. Explain the three methods of passing arguments to functions/events in PB

a) By Value – a copy of the variable is passed. Any changes to the value of the variable will affect the copy only, the original variable in the calling script is not affected
b) By Reference – a pointer to the variable is passed to the function/event. Any changes affect the original variable in the calling script
c) READ-ONLY – a copy of the variable treated as a CONSTANT is available to the function/event

23. Differentiate between instance and shared variables in PB
a) Instance variables are created when the object is created and destroyed when the object is destroyed while a shared variable is created when the FIRST instance of the object is created and is destroyed when the application is closed
b) The value of an instance variable in each instance is independent of its value in other instances while changing the value of a shared variable in one instance will affect other instances

24. Mention some features of N-Up, Composite & CrossTab DW presentation styles
a) N-Up: two or more rows of data displayed next to each other across the page. It is useful for periodic data such as data for each day/week or each month in the quarter
b) CrossTab: - provides a data summary in a row and column format. Data to be selected from one or more tables, DW cannot be external. Crosstab functions can be used for filters, validation rules or computed fields
c) Composite: - it consists of one or more nested reports. It also serves as a container for other reports and has no data source of its own. The user can specify one DW object to be shown on screen, as many reports as the number of DW objects can be viewed on screen based on the retrieval arguments specified by the user

25. Explain some performance considerations that you as a developer would like to review while designing client/server (PB/Sybase) applications
An important consideration is the usage of COMMIT/CONNECT statements to maximize performance and limit locking and resource use. Two design considerations that should be taken care are:
a) Long running connections – if these are NOT acceptable then the application should connect to the database only when necessary. If acceptable then COMMITs should be issued as often as possible so that the changes do in fact occur. More importantly COMMITs should be issued to release any locks placed on DB entities as a result of statements executed during the transaction
b) Settrans/Settransobject function – if the application functionality requires connections to be kept open and issue periodic COMMITs then Settransobject () should be used or use Settrans () for many short-lived transactions

26. Explain the usage of Settransobject function with composite DWs
Only this function should be used for composite presentation styles acting as containers for other DW objects. If settrans () is used with each DW in a composite DW then disconnect does not occur until PB session ends. It should be used only for pure retrieval when DB locks need not be held on tables in other words update () functions are not used.

27. Explain function overloading with an example
It is a feature in PB where a function is defined with the same name as another. The two functions may differ in the number of arguments and also the type of arguments. An example is the Messagebox () function.

28. Explain the two classes of PB user objects and their sub types
Uos are custom visual objects that you can build to supplement standard PB objects. UOs can request/display information and respond to mouse or keyboard actions and create a tab page UO.
a) Visual UO – a reusable control/set of controls. For example a set of buttons to function as a unit having scripts associated with them for standard processing. Three types are:
1. Standard – inherited from a specific visual control. For example command button/checkbox etc
2. Custom - inherited from the userobject system class. You can include many controls in the UO and write scripts for these events.
3. External - it is a UO that displays a visual control defined in a DLL.
b) Class UO – they consist of properties, functions, and events with no visual components.
1. Standard – inherited from a NV PB object such as a transaction/error object, which can have instance variables and functions.
2. Custom – an object of your own design for which you define variables, events and functions in order to encapsulate application-specific programming in an object

29. How do you change the SQL statement of a DW at run-time?
It can be done by linking the DW control to modify () function or using “. Object” notation

30. Can you use an array as an argument to the DW’s Retrieve () function?
Yes, it can be used when your DWs data source contains a Select statement with an IN clause.

31. Application functionality would like to allow the user to print selected rows. How is this done?
You can copy the selected rows to a data store or a hidden DW control using rowscopy () and print the data store or hidden DW control

32. Explain the DW validation rule
If the data in a column has changed, it checks for the correctness of the value (both data type and data value) in the primary buffer. Wrong data type or data value will trigger the itemerror () event. If the data is correct it triggers itemchanged () event, which if it returns ZERO, triggers itemfocuschanged () event.

33. Explain the following error: “Rows changed between retrieve and update”
It occurs when a user updates the data before you update it. PB detects it when you include the timestamp column in the DW or use “key and updateable columns” in the WHERE clause. The solution to the problem would be to use the reselectrow () function to reselect the row that caused the error and get the latest values for the error row and update the DB again.

34. What is the difference between a computed column and a computed field?
The former is defined as part of the SELECT statement, (for example sum, avg etc) whose values are calculated by the database, while in the latter the PB client calculates the values. If it is a fat client then computed fields are recommended, else for thin clients it is computed column.

35. If the application needs to display rows as soon as they are retrieved, what should be done?
Write code in the retrievrow () event and also set the asynch attibute in the DBParm property in the transaction object

36. How would you retrieve multiple result sets in a single DW?
A DW can retrieve only one result set at a time. To retrieve other result sets, you can change the result set number either by modify () or using object notation making sure the number of columns and data types match the existing DW definition.

37. What is the event from which I can see the exact SQL statement sent to the DB by PowerBuilder?
SQLPreview ()

38. How can you update a DW that has a stored procedure as a data source?
It can be done by going to the update properties in the DW by selecting Rows/Update properties from the menu in the design mode in the DW painter. The tables to be updated can be selected.

39. What are the different types of windows in PB?
They are main, popup; child, response, MDI frame, and MDI frame with microhelp.

40. If you create a response window and open that window in an MDI frame using opensheet (), what would happen?
When you open a window in a MDI frame using opensheet () or opensheetwithparm () the window gets the sheet properties irrespective of the window type. If a response window is opened using the above functions the window will behave like any other sheet having maximise, minimize, close controls etc

41. What is the difference between triggerevent () and postevent ()?
The former executes the specified event’s script right away while the latter posts the request in the operating system’s message queue

42. How can I find out if the PB application is connected to the DB or not?
Use the Dbhandle () function

43. Name three PB pronouns used to reduce hard coding
This, parent, parentwindow & super

44. Differentiate between parent & parentwindow
Parent refers to the PB object where the current object is placed. For example parent in a command button’s script will refer to the window in which the command button is placed. Parentwindow is used to refer to the window for which the current menu is attached

45. I have a window, which has a menu, associated with it. For some reason I have deleted the menu and I am getting any error while trying to open the window. What needs to be done?
Export the window as a SRW and look for the menu name in the file. Once found the menu can be created again and linked to the source window.

46. Explain the different types of embedded SQL that can be used in PB scripting
Given below are the SQL statements in scripts that are possible with Sybase ASE:
a) Transaction Management statements – CONNECT, COMMIT, ROLLBACK and DISCONNECT are used to manage transactions in ASE. If a trigger fails, then a RAISEERROR should be issued in the trigger and not ROLLBACK. PB has got a DBMS specific return code (SQLDBCode = -1) within the transaction object which can be used to throw messages to the user.
b) Non-cursor statements – INSERT/UPDATE/DELETE/SELECT
c) Cursor statements – the user can retrieve ( declare, open, fetch & close cursors) and issue update( update & delete cursors)
d) DB Stored Procedures – they can be used for retrieve, update or both. To execute DDL statements the AutoCommit must be set to TRUE (1), but if it is TRUE, ROLLBACK cannot be issued, hence after completion of the DDL operation it must be set back to FALSE.

47. What is DDE? Which PB object has DDE related events associated with it?
DDE stands for dynamic data exchange by means of which two applications can talk to each other and exchange data between them. Examples are RemoteExec & RemoteSend. A PB window has DDE events associated with it

48. Explain the concepts of embedding and linking
When you embed an object it is saved as part of the OLE container object i.e. any changes to the actual object will not reflect in the embedded object. In case of Linking the original object resides where it was and link information is stored in the OLE container object i.e. any changes to the actual object will reflect in the OLE container object. OCX is an OLE control that implements the component-based architecture.

49. Explain enumerated data types in PB
Enumerated data types are specific to PowerScript. They are used as arguments in functions and also to specify the properties of an object or control. A variable of one of the enumerated data types can be assigned a fixed set of values. For example, the enumerated data type Alignment, which specifies the alignment of text, can be assigned one of the following three values: Center! Left!, and Right!:
For example mle_edit.Alignment=Right!

50. Explain the concept of inheritance in PB
It is a feature that enables you to build windows, user objects, and menus that are derived from existing objects. When you change an ancestor object, the changes are reflected in all the descendants and the descendant inherits the ancestor's scripts. Two main features to be noted here are:
a) Descendant objects - In PB, an object class can be inherited from another class. The inherited or descendent object has all the instance variables, events, and functions of the ancestor. You can augment the descendant by adding more variables, events, and functions. If you change the ancestor, even after editing the descendant, the descendant incorporates the changes.

b) Instantiating - When you instantiate a descendent object, PowerBuilder also instantiates all its ancestor classes. You do not have programmatic access to these ancestor instances, except in a few limited ways, such as when you use the scope operator to access an ancestor version of a function or event script.
51. If you were experiencing a GPF in your application, how would you go about tracking it down?
a) Check library search path in development, required DLL’s, PBL’s in runtime etc
b) If PFC is used, check that the PB version is exactly the same as PFC version, i.e. 5.0.04 etc
c) Use DLL tracking utility to check executables DLL list
d) Enabling the PB Debug Tracing information and find the last line of code that executed prior to the GPF.

52. Name some of the PFC services.

a) Application (debugging, error message, security)
b) Data window (filter, linkage, print preview, resize, sorting)
c) Window (menu, resize, file, metaclass)
53. Explain the type of Inheritance.
two types of Inheritance: Single Inheritance and Multi-level Inheritance.
54. Is PowerBuilder support Multiple Inheritance?
No,But you need`multiple inheritance then you can inherit one object from other and You make one object as userobject and then use this userobject inherited object.
55. How many event support an application?
Six even support an application.
open(),close(),connectionbegin(),connectionend(),idle(),systemerror().

Enjoy, Entertain and Learn Something

PowerBuilder frequently asked questions by top companies

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What would be the row status in the destination DataWindow when a row is copied from another DataWindow using RowsCopy() function? Answer

NewModified!

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What would be the row status in the destination DataWindow when a row is copied from another DataWindow using RowsMove() function?

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NewModified!

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Question 39

What would be the row status in the destination DataWindow when a row is copied from another DataWindow using RowsCopy() function?

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