Simple Example of Cursor

This is the simplest example of the SQL Server Cursor. I have used this all the time for any use of Cursor in my T-SQL.
DECLARE @AccountID INT
DECLARE @getAccountID CURSOR
SET @getAccountID = CURSOR FOR
SELECT Account_ID
FROM Accounts
OPEN @getAccountID
FETCH NEXT
FROM @getAccountID INTO @AccountID
WHILE @@FETCH_STATUS = 0
BEGIN
PRINT @AccountID
FETCH NEXT
FROM @getAccountID INTO @AccountID
END
CLOSE @getAccountID
DEALLOCATE @getAccountID

SQL SERVER – Query to Display Foreign Key Relationships and Name of the Constraint for Each Table in Database

This is very long query. Optionally, we can limit the query to return results for one or more than one table.

SELECT
K_Table = FK.TABLE_NAME,
FK_Column = CU.COLUMN_NAME,
PK_Table = PK.TABLE_NAME,
PK_Column = PT.COLUMN_NAME,
Constraint_Name = C.CONSTRAINT_NAME
FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS C
INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS FK ON C.CONSTRAINT_NAME = FK.CONSTRAINT_NAME
INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS PK ON C.UNIQUE_CONSTRAINT_NAME = PK.CONSTRAINT_NAME
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE CU ON C.CONSTRAINT_NAME = CU.CONSTRAINT_NAME
INNER JOIN (
SELECT i1.TABLE_NAME, i2.COLUMN_NAME
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS i1
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE i2 ON i1.CONSTRAINT_NAME = i2.CONSTRAINT_NAME
WHERE i1.CONSTRAINT_TYPE = 'PRIMARY KEY'
) PT ON PT.TABLE_NAME = PK.TABLE_NAME
---- optional:
ORDER BY
1,2,3,4
WHERE PK.TABLE_NAME='something'WHERE FK.TABLE_NAME='something'
WHERE PK.TABLE_NAME IN ('one_thing', 'another')
WHERE FK.TABLE_NAME IN ('one_thing', 'another')

Reference : Pinal Dave (http://blog.SQLAuthority.com)

SQL SERVER – 2005 – Explanation of TRY…CATCH and ERROR Handling

SQL Server 2005 offers a more robust set of tools for handling errors than in previous versions of SQL Server. Deadlocks, which are virtually impossible to handle at the database level in SQL Server 2000, can now be handled with ease. By taking advantage of these new features, you can focus more on IT business strategy development and less on what needs to happen when errors occur. In SQL Server 2005, @@ERROR variable is no longer needed after every statement executed, as was the case in SQL Server 2000. SQL Server 2005 provides the TRY…CATCH construct, which is already present in many modern programming languages. TRY/CATCH helps to write logic separate the action and error handling code. The code meant for the action is enclosed in the TRY block and the code for error handling is enclosed in the CATCH block. In case the code within the TRY block fails, the control automatically jumps to the CATCH block, letting the transaction roll back and resume execution. In addition to this, the CATCH block captures and provides error information that shows you the ID, message text, state, severity and transaction state of an error.

Functions to be used in CATCH block are :

  • ERROR_NUMBER: returns the error number, and is the same value of @@ERROR.
  • ERROR_SEVERITY: returns the severity level of the error that invoked the CATCH block.
  • ERROR_STATE: returns the state number of the error.
  • ERROR_LINE: returns the line number where the error occurred.
  • ERROR_PROCEDURE: returns the name of the stored procedure or trigger for which the error occurred.
  • ERROR_MESSAGE: returns the full message text of the error. The text includes the values supplied for any substitutable parameters, such as lengths, object names, or times.

You can use these functions anywhere inside a CATCH block, and they will return information regarding the error that has occurred. These functions will return the value null outside of the CATCH block.

Syntax:
BEGIN TRY
{ sql_statement |
statement_block }
END TRY
BEGIN CATCH
{ sql_statement |
statement_block }
END CATCH

The TRY or CATCH block can contain a single T-SQL statement or a series of statements. The CATCH block must follow immediately after the TRY block. The TRY/CATCH block cannot span more than a single batch. In addition, TRY/CATCH block cannot span an IF/ELSE statement.

Example of TRY…CATCH:
BEGIN TRY
DECLARE @X INT
---- Divide by zero to generate Error
SET @X = 1/0
PRINT 'Command after error in TRY block'
END TRY
BEGIN CATCH
PRINT 'Error Detected'
END CATCH
PRINT 'Command after TRY/CATCH blocks'

Above code will return following result:

Error Detected
Command after TRY/CATCH blocks


If all the statements within the TRY block are executed successfully, then processing does not enter the CATCH block, but instead skips over the CATCH block and executes the first statement following the END CATCH statement. Removing SET statement in above code PRINT ‘Error Detected’ statement is not executed, but the PRINT statement within the TRY block is executed, as well as the PRINT statement after the TRY/CATCH block. TRY/CATCH blocks can be nested.

Limitation of TRY…CATCH:

  • Compiled errors are not caught.
  • Deferred name resolution errors created by statement level recompilations. (If process is terminated by Kill commands or broken client connections TRY…CATCH will be not effective)
  • Errors with a severity greater than 10 that do not terminate their database connection are caught in the TRY/CATCH block.

For errors that are not trapped, SQL Server 2005 passes control back to the application immediately, without executing any CATCH block code.

Similar example of TRY…CATCH which includes all the ERROR functions:
USE AdventureWorks;
GO
BEGIN TRY
-- Generate a divide-by-zero error.
SELECT 1/0;
END TRY
BEGIN CATCH
SELECT
ERROR_NUMBER() AS ErrorNumber,
ERROR_SEVERITY() AS ErrorSeverity,
ERROR_STATE() AS ErrorState,
ERROR_PROCEDURE() AS ErrorProcedure,
ERROR_LINE() AS ErrorLine,
ERROR_MESSAGE() AS ErrorMessage;
END CATCH;
GO

Reference : Pinal Dave (http://blog.SQLAuthority.com) , BOL

SQL SERVER – Retrieve – Select Only Date Part From DateTime – Best Practice

Just a week ago my Database Team member asked me what is the best way to only select date part from datetime. When ran following command it also provide the time along with date.
SELECT GETDATE()

ResuleSet:
2007-06-10 7:00:56.107

The required outcome was only 2007/06/10.

I asked him to come up with solution by using date functions. The method he suggested was to use
SELECT DATEADD(D, 0, DATEDIFF(D, 0, GETDATE()))

I approved his method though, I finally suggested my method using function CONVERT.
SELECT CONVERT(VARCHAR(10),GETDATE(),111)

The reason I use this because it is very convenient as well as provides quick support to convert the date in any format. The table which suggest many format are displayed on MSDN.

Some claims that using CONVERT is slower then using DATE functions but it is extremely negligible. I prefer to use CONVERT.

Reference : Pinal Dave (http://blog.SQLAuthority.com)