Skip to main content

Constraints in sql server

Constraints - Constraints are the rules enforced on data columns on table. This ensures the accuracy and reliability of the data in the database. Constraints define some conditions that restricts the column to remain true while inserting or updating or deleting data in column.

Constraints can be defined in two ways 
1) The constraints can be specified immediately after the column definition.
This is called column-level definition. 
2) The constraints can be specified after all the columns are defined.
This is called table-level definition. 

Types of Constraints in SQL-Server

NOT NULL- This constraint is responsible for a column to confirm that a column cannot have a null value.

DEFAULTThis constraint provides a default value when specified non for this column.

UNIQUE- This constraint insure that each row for the column has different value.

PRIMARY KEY- Primary key constraint is a combination of a NOT NULL constraint and a UNIQUE constraint. This constraint ensures that the specific column for a table have an unique identity.

FOREIGN KEY- this constraints responsible to uniquely identified a rows/records in any another database table.

CHECK- The CHECK responsible to enables a condition to check the value being entered into a record


Popular posts from this blog

TRY/CATCH and error handling in SQL server 2005/2008

SQL Server 2005 provide a strong set of tool to handle error or exception, in privious version it was not easy to handle exceptions. We use TRY/CATCH in SQL Server same as populer languages, We write saperate logic and exception handling code. Syntax: BEGIN TRY -- Your Code or query END TRY BEGIN CATCH -- Handling code END CATCH We write our logic code within TRy bolck and exception code in CATCh block, if nay error occur in logic code it jumps to CATCH  block, resume the execution and transaction is rollback. Functions which is use in CATCH 1- ERROR_NUMBER() Returns error no othe error message. 2- ERROR_SEVERITY() returns the error severity regardless of how many times it is run. 3- ERROR_STATE() Returns the state number of error messages that cause the catch block. 4- ERROR_PROCEDURE() Return the Procedure Name. 5- ERROR_LINE() Return error line number. 6- ERROR_MESSAGE() return error description. Note : If we are calling all above method out side from C

remove special characters from string in sql server

Using This Query you can remove special characters from string in sql DECLARE @str VARCHAR ( 400 )     DECLARE @expres  VARCHAR ( 50 ) = '%[~,@,#,$,%,&,*,(,),.,!]%'       SET @str = '(remove) ~special~ *characters. from string in sql!'       WHILE PATINDEX ( @expres , @str ) > 0           SET @str = Replace ( REPLACE ( @str , SUBSTRING ( @str , PATINDEX ( @expres , @str ), 1 ), '' ), '-' , ' ' )       SELECT @str