In MySQL, the CHECK constraint is used to put limit on value range on value inside a column.

CHECK Constraint on CREATE TABLE

The following statement creates a CHECK constraint on the "id" column when the "employee" table is created. The CHECK constraint specifies that the column "id" should only include integer values greater than 0:

Example:

CREATE TABLE employee
(
id int NOT NULL,
first_name varchar(45) NOT NULL,
last_name varchar(45),
country varchar(45),
CHECK (id>0)
);

We can also define CHECK constraint on multiple column, for this use the below statement:

CREATE TABLE emplyee
(
id int NOT NULL,
first_name varchar(45) NOT NULL,
last_name varchar(45),
country varchar(45),
CONSTRAINT chk_Person CHECK (id>0 AND country='Canada')
);

CHECK Constraint on ALTER TABLE

We can also create CHECK constraint on a column when the table is already created, for that we use ALTER command.

ALTER TABLE employee
ADD CHECK (id>0);

Similarly we can define CHECK constraint on multiple columns when the table is already created as below:

ALTER TABLE employee
ADD CONSTRAINT chk_employee CHECK (id>0 AND country='Canada');

To DROP a CHECK Constraint

We can also drop a CHECK constraint. To drop a CHECK constraint, use the below statement:

ALTER TABLE employee
DROP CHECK chk_employee;

Hope this will help you :)