SQL CHECK Keyword

CHECK

The CHECK constraint limits the value that can be placed in a column.

SQL CHECK on CREATE TABLE

The following SQL creates a CHECK constraint on the "Age" column when the "Persons" table is created. The CHECK constraint ensures that you can not have any person below 18 years:

CREATE TABLE Persons
(

   
Age int,

   
CHECK (Age>=18)

);

CREATE TABLE Persons
(

   
Age int CHECK (Age>=18)

);

MySQL:

SQL Server / Oracle / MS Access:

To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:

CREATE TABLE Persons
(

   
Age int,

   
City varchar(255),

   
CONSTRAINT CHK_Person CHECK (Age>=18 AND City='Sandnes')

);

MySQL / SQL Server / Oracle / MS Access:

SQL CHECK on ALTER TABLE

To create a CHECK constraint on the "Age" column when the table is already created, use the following SQL:

ALTER TABLE Persons

ADD CHECK (Age>=18);

MySQL / SQL Server / Oracle / MS Access:

To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:

ALTER TABLE Persons

ADD CONSTRAINT CHK_PersonAge CHECK (Age>=18 AND City='Sandnes');

MySQL / SQL Server / Oracle / MS Access:

DROP a CHECK Constraint

To drop a CHECK constraint, use the following SQL:

ALTER TABLE Persons

DROP CONSTRAINT CHK_PersonAge;

ALTER TABLE Persons

DROP CHECK CHK_PersonAge;

SQL Server / Oracle / MS Access:

MySQL: