SQL CHECK
SQL CHECK constraints
CHECK constraints are used to limit the range of values in a column.
If a CHECK constraint is defined on a single column, only specific values are allowed for that column.
If a CHECK constraint is defined on a table, the constraint limits values in a specific column based on the values of other columns in the row.
SQL CHECK constraint when CREATE TABLE
The following SQL creates a CHECK constraint on the "P_Id" column when the "Persons" table is created. The CHECK constraint states that the "P_Id" column must contain only integers greater than 0.
MySQL：
(
P_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:
(
P_Id int NOT NULL CHECK (P_Id>0),
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
If you need to name the CHECK constraint, and define it For CHECK constraints on multiple columns, please use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
(
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 when ALTER TABLEWhen the table has When created, to create a CHECK constraint on the "P_Id" column, use the following SQL:
MySQL / SQL Server / Oracle / MS Access:
MySQL / SQL Server / Oracle / MS Access:
Revoke CHECK constraintTo revoke CHECK constraint, please use the following SQL:
SQL Server / Oracle / MS Access ：
ALTER TABLE Persons
