SQL check constraint
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.
SYNTAX :
CREATE TABLE Emp ( E_Id int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255), CHECK (P_Id>0) )
SQL Server / Oracle / MS Access:
CREATE TABLE Emp ( E_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 Emp ( E_Id int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255), CONSTRAINT chk_Employee CHECK (E_Id>0 AND City='Sandnes') );