SQL Check
SQL CHECK Constraint
The value range that can be entered into a column is restricted by the CHECK constraint.
A column that has a CHECK constraint defined on it will only accept specific values.
A table’s CHECK constraint might restrict values in specific columns according to values in other columns in the row.
SQL CHECK on CREATE TABLE
Upon creating the “Persons” table, the following SQL places a CHECK constraint on the “Age” field. The CHECK constraint guarantees that an individual must be eighteen years of age or older:
MySQL:
------ EXAMPLE MUKAVU ------
SQL Server / Oracle / MS Access:
------ EXAMPLE MUKAVU ------
Use the following SQL syntax to define a CHECK constraint on multiple columns and to allow naming of the constraint:
MySQL / SQL Server / Oracle / MS Access:
------ EXAMPLE MUKAVU ------
SQL CHECK on ALTER TABLE
When the table has already been established, use the following SQL to create a CHECK constraint on the “Age” column:
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ADD CHECK (Age>=18);
Use the following SQL syntax to define a CHECK constraint on multiple columns and to allow naming of the constraint:
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ADD CONSTRAINT CHK_PersonAge CHECK (Age>=18 AND City='Sandnes');
DROP a CHECK Constraint
To remove a CHECK constraint, use the SQL code below:
SQL Server / Oracle / MS Access:
ALTER TABLE Persons
DROP CONSTRAINT CHK_PersonAge;
MySQL:
ALTER TABLE Persons
DROP CHECK CHK_PersonAge;
