MySQL CHECK Constraint
In MySQL, CHECK constraint controls the values in the associated column. In other words, CHECK constraints ensures that the value in a certain column satisfy a Boolean expression or not.
MySQL CHECK Constraint example
The following MySQL, creates a
CHECK constraint on the "Age" column when the "tblCustomer" table is created. The
CHECK constraint ensures that the customer's age greater or equal to 18 years:
Example
CREATE TABLE tblCustomer (
custId int NOT NULL,
firstName varchar(255) NOT NULL,
lastName varchar(255) NOT NULL,
Age int,
CHECK (Age>=18)
);
MySQL CHECK Constraint on ALTER table example
The following MySQL, creates a
CHECK constraint on the "Age" column when table already exists into the database:
Example
ALTER TABLE tblCustomer
ADD CHECK (Age>=18);
OR
ALTER TABLE tblCustomer
ADD CONSTRAINT CHK_CustomerAge CHECK (Age>=18);
MySQL DROP a CHECK Constraint example
The following MySQL, dropping
CHECK constraint "UC_Customer" from "tblCustomer" table:
Example
ALTER TABLE tblCustomer
DROP CHECK CHK_CustomerAge;