Check in DBMS

Example for check constraint

CREATE TABLE STUDENT (
    ID int ,
    Name varchar(255) ,
    Age int,
    CHECK (Age>=18)
); 

• As we have used a check constraint as (Age>=18) which means values entered by the user for this age column while inserting the data must be less than or equal to 18 otherwise an error is shown 
• Simply, the only possible values that the age column will accept is [0 -17].

Check constraint at table level

CREATE TABLE student {
   ID int ,
   Name varchar(255) ,
   Program interface specificationAge int,
   City varchar(255),
   CONSTRAINT CHK_Person CHECK (Age>=18 AND City='hyderabad')
); 

• You can apply check constraint to more than one column at a time 
• In the above example we have used two conditions with the check constraint Age>=18 AND City=’ Hyderabad’ , as a result, both the columns age and city will be checked while data is entered  i.e the only possible values that are accepted for the column age are 0 -17 and city must be only Hyderabad