SQLCHECK Keyword
CHECK
TheCHECK 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:
MySQL:
Age int,
CHECK (Age>=18)
);
SQL Server / Oracle / MS Access:
Age int CHECK (Age>=18)
);
To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
Age int,
City varchar(255),
CONSTRAINT CHK_Person CHECK (Age>=18 AND City='Sandnes')
);
SQL CHECK on ALTER TABLE
To create a CHECK constraint on the "Age" column when the table is already created, use the following SQL:
MySQL / SQL Server / Oracle / MS Access:
ADD CHECK (Age>=18);
To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
ADD CONSTRAINT CHK_PersonAge CHECK (Age>=18 AND City='Sandnes');
DROP a CHECK Constraint
To drop a CHECK constraint, use the following SQL:
SQL Server / Oracle / MS Access:
DROP CONSTRAINT CHK_PersonAge;
MySQL:
DROP CHECK CHK_PersonAge;
