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  • Check Constraint

    @suresh.ramola
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    Check Constraint:

    It is used to restrict the range of values that can be inserted in a column. If a column contain check constraint then only a particular range of values can be inserted in that column.

    Example:

    1. CREATE TABLE Employee(
    2.        Emp_ID   INT              NOT NULL,
    3.        Emp_NAME VARCHAR (20)     NOT NULL,
    4.        Emp_AGE  INT              NOT NULL CHECK (Emp_AGE >= 18),
    5.        Emp_ADDRESS  CHAR (25) ,
    6.        Emp_SALARY   DECIMAL (18, 2),       
    7.        PRIMARY KEY (Emp_ID)
    8. );

    In this example we have put check constraint on Emp_Age column and we cannot insert Employee whose age is less than 18.

    Adding Check Constraint using Alter Command:

    We can easily add Check constraint  using Alter command.

    1. ALTER TABLE Employee
    2.    ADD CONSTRAINT myCheck CHECK (Emp_AGE >= 18 );
    3.  

    Drop a Check Constraint:

    1. ALTER TABLE Employee
    2.    DROP CONSTRAINT myCheck;

     

    SQL Oracle
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