Usage and examples of SQL DROP CONSTRAINT keyword

SQL Keyword Reference

DROP CONSTRAINT (Delete constraint)

The DROP CONSTRAINT command is used to delete UNIQUE, PRIMARY KEY, FOREIGN KEY, or CHECK constraints.

Delete UNIQUE constraint

To delete the UNIQUE constraint, please use the following SQL:

SQL Server / Oracle / MS Access：

ALTER TABLE Persons
DROP CONSTRAINT UC_Person;

MySQL：

ALTER TABLE Persons
DROP INDEX UC_Person;

Delete PRIMARY KEY constraint

To delete the PRIMARY KEY constraint, please use the following SQL:

SQL Server / Oracle / MS Access：

ALTER TABLE Persons
DROP CONSTRAINT PK_Person;

MySQL：

ALTER TABLE Persons
DROP PRIMARY KEY;

Delete FOREIGN KEY Constraint

To delete a FOREIGN KEY constraint, use the following SQL:

SQL Server / Oracle / MS Access：

ALTER TABLE Orders
DROP CONSTRAINT FK_PersonOrder;

MySQL：

ALTER TABLE Orders
DROP FOREIGN KEY FK_PersonOrder;

Delete CHECK Constraint

To delete a CHECK constraint, use the following SQL:

SQL Server / Oracle / MS Access：

ALTER TABLE Persons
DROP CONSTRAINT CHK_PersonAge;

MySQL：

ALTER TABLE Persons
DROP CHECK CHK_PersonAge;

SQL Keyword Reference