Database Knowledge

Life Quote

2015-04-12T21:55:00.001-07:00

Life Quote: The difficulties, hardships and trials of life, the obstacles...are positive blessings. They knit the muscles more firmly, and teach self-reliance. ~ William Matthews

SAP FI Practice

2015-04-10T08:59:00.002-07:00

If you are working with SAP in the module FICO, you can use this one to practice http://languagexyz.appspot.com/sapfi
It looks like the following and you can run on your smartphone or tablet.

Better Decisions with Smarter Data | MIT Sloan Management Review

2014-02-22T20:19:00.001-08:00

Better Decisions with Smarter Data | MIT Sloan Management Review:

Accurate – data must be what it says it is with enough precision to drive value. Data quality matters.
Actionable – data must drive an immediate scalable action in a way that maximizes a business objective like media reach across platforms. Scalable action matters.
Agile – data must be available in real-time and ready to adapt to the changing business environment. Flexibility matters.

Agile Principles and Values, by Jeff Sutherland

2014-01-22T07:36:00.001-08:00

Agile Principles and Values, by Jeff Sutherland

PostgreSQL: Replace multiple spaces with one

2013-01-01T08:48:00.000-08:00

If you want to use a single query to replace multiple spaces with one on SQL Server, you can read the articles here http://www.sqlservercentral.com/articles/T-SQL/68378/
However, it's very simple in PostgreSQL by using Regular Expression
SELECT regexp_replace('This sentence contains multiple spaces', '\s+', ' ', 'g');

PostgreSQL - Copy CSV to table with psql - part 2

2012-12-30T20:08:00.004-08:00

CREATE TABLE tbl_test
(
 a text,
 b text,
 c text
)

Content of test.csv, and it put in /Database folder
a1,b1,c1
a2,b2,c2
a3,b3,c3

Instead of using COPY command directly, you can modify the test.cvs file to include it, as
COPY tbl_test FROM STDIN WITH CSV;
a1,b1,c1
a2,b2,c2
a3,b3,c3
\.

Note that you have to include a carriage return in the last line of the file (after '\.')
Then, run the following command to import

MyComputer$ psql -h localhost -p 5432 -U postgres testdb -f ~/Database/test.csv

PostgreSQL - Copy database

2012-12-13T07:41:00.002-08:00

Sometimes, instead of back up and restore to a new db and wait your time if you only want to copy a database and put in the same server, you can use the following query:

CREATE DATABASE newdb WITH TEMPLATE originaldb OWNER dbuser;

Note that this query only successfully if no sessions existing in originaldb. So, you can check originaldb sessions and kill them with this function pg_terminate_backend(procpid)

PostgreSQL - Kill idle processes

2012-12-13T06:43:00.003-08:00

Sometimes, you need to kill all unnecessary processes running on your database server. You can do that by using the following query:

SELECT           
   procpid,
   (
       SELECT pg_terminate_backend(procpid)
   ) AS killed
 FROM pg_stat_activity
 WHERE current_query LIKE '%idle%' AND datname = 'YourDBName';

PostgreSQL - Copy csv file to table with psql

2012-12-09T07:54:00.000-08:00

CREATE TABLE tbl_test
(
 a text,
 b text,
 c text
)

Content of test.csv
a1,b1,c1
a2,b2,c2
a3,b3,c3

psql to COPY
psql -h localhost -U postgres testdb
testdb=# COPY tbl_test FROM 'D:\Temp\test.csv' WITH DELIMITER ',' CSV;

PostgreSQL - VACUUM ANALYZE EXPLAIN NOTIFY

2012-12-09T06:35:00.003-08:00

Select the correct statement that records the space occupied by deleted or updated rows for later reuse, and also updates statistics.

A. VACUUM
B. VACUUM ANALYZE
C. EXPLAIN
D. EXPLAIN ANALYZE
E. NOTIFY
F. None of the above

Answer: [B]
Highlight to find out the answer.

PostgreSQL - ANALYZE quiz

2012-12-09T06:15:00.000-08:00

What does the following command do?
Choose the correct answer below.
Note: "psql=#" is the command prompt for psql.
psql=# ANALYZE xyz;

A. Collects statistical information related to the content of the database xyz.
B. Collects statistical information related to the content of the table xyz.
C. Outputs statistical information related to the content of the table xyz.
D. No ANALYZE command in PostgreSQL, error will occur.
E. None of the above
F. Both B & C

Answer: [B]
Highlight to find out the answer.

PostgreSQL – Convert rows to string

2012-12-07T09:14:00.001-08:00

SELECT array_to_string(
    array(
        SELECT name
        FROM pg_settings
        WHERE setting = 'off' AND context = 'postmaster'
    ), ',');

SELECT setting, array_to_string(array_agg(name), ',')
FROM pg_settings
WHERE setting IN ('on', 'off')
GROUP BY setting;

PostgreSQL - Query data from another database/server

2012-11-24T09:02:00.002-08:00

Assume that, you have two databases:
1. db1 with two schemas: public and sch1
2. db2 with two schemas: public and sch2

In PostgreSQL, you can access a table from a different schema by using SELECT * FROM schema_name.table_name such as SELECT * FROM db1_sch.employee;
However, you cannot access a table on the different database with explicit way like SELECT * FROM db2.sch2.employee;

The question is how can we access like SQL Server or some other DBMS.
Fortunately, PostgreSQL support dblink to do that.

First, install extension dblink on the database you want to be able to access to other
CREATE EXTENSION dblink;

If db2 is in the same server, you can query table in db2 like that:
SELECT *
FROM dblink('dbname=db2', 'SELECT employee_id, employee_name FROM sch2.employee')
AS employee(employee_id integer, employee_name text);

If db2 is in the different server, you can query:
SELECT *
FROM dblink('hostaddr=172.x.x.x dbname=db2 user=admin password=pwd port=5432', 'SELECT employee_id, employee_name FROM sch2.employee')
AS employee(employee_id integer, employee_name text);

PostgreSQL - get table structure

2012-11-05T07:20:00.001-08:00

SELECT ordinal_position
, column_name
, CASE data_type WHEN 'character varying' THEN data_type || '('||character_maximum_length || ')' ELSE data_type END data_type
, column_default
, is_nullable
, character_maximum_length
, numeric_precision
FROM information_schema.columns
WHERE table_catalog = 'database_name'
AND table_schema = 'schema_name'
AND table_name = 'table_name'
ORDER BY ordinal_position;

PostgreSQL: check the core settings of server

2012-10-19T01:02:00.001-07:00

SELECT name, context, unit, setting, short_desc

FROM pg_settings

WHERE name in ('listen_addresses' ,'max_connections' ,'shared_buffers' ,'effective_cache_size' , 'work_mem' , 'maintenance_work_mem')

ORDER BY context,name;

If context is set to postmaster, it means changing this parameter requires a restart of the postgresql service. If context is set to user, changes require at least a reload. Furthermore, these settings can be overridden at the database, user, session, or function levels.

unit tells you the unit of measurement that the setting is reported in. This is very important for memory settings since, as you can see, some are reported in 8 kB and some in kB

PosgreSQL: get main configuration files

2012-10-18T00:36:00.001-07:00

SELECT name, setting FROM pg_settings WHERE category = 'File Locations';

postgresql.conf controls general settings, such as how much memory to allocate, default storage location for new databases, which IPs PostgreSQL listens on, where logs are stored, and so forth.

pg_hba.conf controls security. It manages access to the server, dictating which users can login into which databases, which IPs or groups of IPs are permitted to connect and the authentication scheme expected.

pg_ident.conf is the mapping file that maps an authenticated OS login to a PostgreSQL user. This file is used less often, but allows you to map a server account to a PostgreSQL account. For example, people sometimes map the OS root account to the postgre’s super user account. Each authentication line in pg_hba.conf can use a different pg_ident.conf file

PostgreSQL quiz: stored procedure execution

2012-10-17T23:39:00.001-07:00

Assume that you have a table contact and a stored procedure called insert_contact as the following screenshots

Which one below is correct?

A. CALL insert_contact(‘John’,'Tran’);

B. EXECUTE insert_contact(‘John’,’Tran’);

C. SELECT insert_contact(‘John’,’Tran’)

D. Both A & B

E. Error in the store procedure code

F. None of the above

Answer: [C]

Highlight to find out the answer.

PostgreSQL license

2012-10-16T00:44:00.001-07:00

Select the most suitable statement about the PostgreSQL license from below.

A. PostgreSQL is distributed under the GPL license.
B. PostgreSQL is distributed under the PostgreSQL license.
C. PostgreSQL is distributed under the LGPL license.
D. PostgreSQL is distributed under the BSD license.
E. PostgreSQL is distributed under the X11(MIT) license.

Answer: [D]

Highlight to find out the answer.

Convert date time values to string in PostgreSQL

2012-10-15T22:55:00.001-07:00

This is a view extracted from OpenERP.

CREATE OR REPLACE VIEW crm_claim_report
AS
SELECT min(c.id) AS id
, to_char(c.date, 'YYYY'::text) AS name
, to_char(c.date, 'MM'::text) AS month
, to_char(c.date, 'YYYY-MM-DD'::text) AS day
, to_char(c.date_closed, 'YYYY-MM-DD'::text) AS date_closed
, to_char(c.date_deadline::timestamp with time zone, 'YYYY-MM-DD'::text) AS date_deadline, c.state, c.user_id
, c.stage_id, c.section_id, c.partner_id, c.company_id, c.categ_id, count(*) AS nbr, c.priority
, c.type_action, date_trunc('day'::text, c.create_date) AS create_date
, avg(date_part('epoch'::text, c.date_closed - c.create_date)) / (3600 * 24)::double precision AS delay_close
, ( SELECT count(mailgate_message.id) AS count FROM mailgate_message
WHERE mailgate_message.model::text = 'crm.claim'::text AND mailgate_message.res_id = c.id AND mailgate_message.history = true) AS email
, ( SELECT avg(crm_case_stage.probability) AS avg FROM crm_case_stage
WHERE crm_case_stage.type::text = 'claim'::text AND crm_case_stage.id = c.stage_id) AS probability
, date_part('epoch'::text, c.date_deadline::timestamp without time zone - c.date_closed) / (3600 * 24)::double precision AS delay_expected
FROM crm_claim c
GROUP BY to_char(c.date, 'YYYY'::text), to_char(c.date, 'MM'::text), to_char(c.date, 'YYYY-MM-DD'::text), c.state, c.user_id, c.section_id
, c.stage_id, c.categ_id, c.partner_id, c.company_id, c.create_date, c.priority, c.type_action, c.date_deadline, c.date_closed, c.id;

PostgreSQL Contactenation

2012-10-14T04:24:00.000-07:00

Which query is correct in PostgreSQL?

A. SELECT 'Test' . 'query';
B. SELECT cat('Test','query') FROM dual;
C. SELECT 'Test' + 'query';
D. SELECT 'Test' + 'query' FROM dual;
E. SELECT 'Test' || 'query';

Answer:[E]
Highlight to find out the answer.

Same query for Fiscal and Normal calendar

2012-10-12T10:51:00.001-07:00

tblFiscalMapping

Assume that you have a mapping table between Fiscal and Normal calendar above.

Sometimes, you need to write one stored procedure with a param @IsFiscal to determine when to return order info on Fiscal year or Normal calendar year.

You can implement as the following

DECLARE @StartMonth SMALLDATETIME;
DECLARE @EndMonth SMALLDATETIME;

IF ISNULL(@IsFiscal,0) = 0
    SELECT @StartMonth = CAST(CAST(@Year AS VARCHAR) + '-01-01' AS SMALLDATETIME);
ELSE
    SELECT @StartMonth = CAST(CAST([Year] AS VARCHAR) + '-' + CAST(NormalMonth AS VARCHAR) + '-01' AS SMALLDATETIME)
    FROM dbo.tblFiscalMapping
    WHERE FiscalYear = @Year;

SET @EndMonth = DATEADD(m, 11, @StartMonth);

SELECT OrderID, OrderNumber, OrderDate, CustomerID, TotalAmount

FROM dbo.tblOrder

WHERE DATEDIFF(m, @StartMonth, OrderDate) >= 0
AND DATEDIFF(m, @EndMonth, OrderDate) <= 0

Create a Virtual Active Directory Domain Controller with VirtualBox

2012-10-12T08:52:00.001-07:00

I need to query Active Directory by using SQL Server, so I created virtual Active Directory Domain Controller to do that.

1. Install Windows Server virtual machine, such as Windows Server 2003

2. Install Client virtual machine, such as Windows XP

3. Set up network

4. Set up new Adapter for each machine, use the adapter set up on Step 3

5. Run Windows Server machine

6. Install Active Directory by following steps after running dcpromo

7. Set up IP Address on Windows Server, note that IP address must be in the range set up in Step 3

8. Set up IP Address on Client machine

9. Create a domain user for client machine in Domain Controller

To allow domain user as local admin, please visit this link

10. Register client machine in domain controller which is defined in Step 6, then input user name/pwd defined in Step 9

Create SQL Server linked server to PostgreSQL database

2012-10-09T08:34:00.001-07:00

1. Download ODBC Driver at this address http://www.postgresql.org/ftp/odbc/versions/msi/

Choose the suitable version with your PostgreSQL database. I’m using PostgreSQL 9, so I chose latest version. (^_^)

2. Install ODBC Driver for PostgreSQL

3. Create connection to PostgreSQL database with ODBC Driver

4. Now, it’s time to create linked server to PostgreSQL database:

You can create with GUI

Or can create with scripts

EXEC master.dbo.sp_addlinkedserver @server = N'OPENERP', @srvproduct=N'PostgreSQL', @provider=N'MSDASQL', @datasrc=N'OpenERP';

GO
EXEC master.dbo.sp_addlinkedsrvlogin @rmtsrvname=N'OPENERP',@useself=N'False',@locallogin=NULL,@rmtuser=NULL,@rmtpassword=NULL;

Finally, you can query PostgreSQL database inside SQL Server

5. Verify the linked server

Query Excel spreadsheet on SQL Server 2008 64 bit with Linked Server

2012-10-09T05:46:00.001-07:00

For SQL Server 64 bit, if you use Microsoft.Jet.OLEDB.4.0, you may experience this issue:

OLE DB provider 'Microsoft.Jet.OLEDB.4.0' cannot be used for distributed queries because the provider is configured to run in single-threaded apartment mode.

To fix this, please follow the following:

1. Download and install Microsoft Access Database Engine 2010 Redistributable at this address http://www.microsoft.com/en-us/download/details.aspx?id=13255

2. After installing, create a linked server to your Excel file

EXEC master.dbo.sp_addlinkedserver @server = N'EXCEL_LINKED_SERVER_NAME'
                    , @srvproduct=N'Excel'
                    , @provider=N'Microsoft.ACE.OLEDB.12.0'
                    , @datasrc=N'C:\Your_Excel_File.xls'
                    , @provstr=N'Excel 12.0';

EXEC master.dbo.sp_addlinkedsrvlogin @rmtsrvname=N'EXCEL_LINKED_SERVER_NAME',@useself=N'False',@locallogin=NULL,@rmtuser=NULL,@rmtpassword=NULL;

3. Run OPENQUERY to get data from your Excel file

SELECT * FROM OPENQUERY(EXCEL_LINKED_SERVER_NAME,'SELECT * FROM [Sheet1$]')

Get current queries executing on PostgreSQL

2012-10-08T08:11:00.000-07:00

SELECT datname "Database Name"
, usename "User Name"
, procpid "Process ID"
, client_addr "Client IP Address"
, waiting "Is waiting"
, query_start "Start Time"
, current_query "Query Text"
FROM pg_stat_activity;