check constraint

check constraint

-it can be used limiting by values are accepted one more values.
-it can be used any logical values expression and true or false logical operators.
-CHECK constraints reject values that evaluate to FALSE. Because null values the Database Engine inserts NULL and does not return an error.

Check Constraint:

 CREATE TABLE Test(Id int  constraint Ck_ID check (LEN(ID)=1))

 INSERT INTO Test values(null)

 (1 row(s) affected)

 

 Function Using Check Constraint:

 CREATE TABLE Test2 (ID1 int, ID2 int);

 CREATE FUNCTION CheckingFun()
 RETURNS int
 AS
 BEGIN
 DECLARE @val int
 SELECT  @val=COUNT(*) from Test2
 RETURN  @val
 END;

 ALTER TABLE Test2 ADD CONSTRAINT CH_ID CHECK(dbo.CheckingFun()>=1)

 INSERT INTO Test2 Values(10,10)

 (1 row(s) affected)

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