Check in DBMS

April 22, 2021

Check in DBMS 

 

In this article, we will learn about Check-in DBMS.

  • Suppose in real-time if you want to give access to an application only if the age entered by the user is greater than 18 this is done at the back-end by using a check constraint
  • Check constraint ensures that the data entered by the user for that column is within the range of values or possible values specified.
Syntax for check constraint 
CREATE TABLE STUDENT (
     column1 datatype(size),
     column2 datatype(size),
     column3 datatype(size),
    CHECK (condition)
);
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
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