SQL CHECK Constraint
The CHECK constraint is used to limit the value range that can be placed in a column.If you define a CHECK constraint on a single column it allows only certain values for this column.
If you define a CHECK constraint on a table it can limit the values in certain columns based on values in other columns in the row.
SQL CHECK Constraint on CREATE TABLE
The following SQL creates a CHECK constraint on the "P_Id" column when the "Persons" table is created. The CHECK constraint specifies that the column "P_Id" must only include integers greater than 0.My SQL:
CREATE TABLE Persons ( P_Id int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255), CHECK (P_Id>0) ) |
CREATE TABLE Persons ( P_Id int NOT NULL CHECK (P_Id>0), LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255) ) |
MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Persons ( P_Id int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255), CONSTRAINT chk_Person CHECK (P_Id>0 AND City='Sandnes') ) |
SQL CHECK Constraint on ALTER TABLE
To create a CHECK constraint on the "P_Id" column when the table is already created, use the following SQL:MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons ADD CHECK (P_Id>0) |
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons ADD CONSTRAINT chk_Person CHECK (P_Id>0 AND City='Sandnes') |
To DROP a CHECK Constraint
To drop a CHECK constraint, use the following SQL:SQL Server / Oracle / MS Access:
ALTER TABLE Persons
DROP CONSTRAINT chk_Person