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Using Constraints in Sql Server


Posted Date: 18 Jun 2008    Resource Type: Code Snippets    Category: SQL
Posted By: Kapil Dhawan       Member Level: Gold
Rating:     Points: 4



The list of common constraints is given below


  • Not Null

  • Unique

  • Check

  • Primary Key

  • foreign Key



NOT NULL



By default when we create a column in table, it can take null value. If we want that it should not take null then we use this constraints. The example for NOT NULL constraint is given below


CREATE TABLE TAB_EMPLOYEE 
(
EMP_ID integer NOT NULL, 
EMPNAME varchar (30) NOT NULL 
)



UNIQUE



This constraint is responsible for having unique values in a column. Here is the code sample for UNIQUE constraint:


CREATE TABLE TAB_EMPLOYEE
(
EMP_ID integer UNIQUE, 
EMPNAME varchar(30)
)




CHECK



CHECK constraint ensures that values are according to the conditions


CREATE TABLE TAB_EMPLOYEE
(
EMP_ID integer CHECK(EMP_ID > 0), 
EMPNAME varchar(30)
)








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