SQL DROP CONSTRAINT Keyword

DROP CONSTRAINT

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

DROP a UNIQUE Constraint

To drop a UNIQUE constraint, use the following SQL:

ALTER TABLE Persons

DROP CONSTRAINT UC_Person;

ALTER TABLE Persons

DROP INDEX UC_Person;

SQL Server / Oracle / MS Access:

MySQL:

DROP a PRIMARY KEY Constraint

To drop a PRIMARY KEY constraint, use the following SQL:

ALTER TABLE Persons

DROP CONSTRAINT PK_Person;

ALTER TABLE Persons

DROP PRIMARY KEY;

SQL Server / Oracle / MS Access:

MySQL:

DROP a FOREIGN KEY Constraint

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

ALTER TABLE Orders

DROP CONSTRAINT FK_PersonOrder;

ALTER TABLE Orders

DROP FOREIGN KEY FK_PersonOrder;

SQL Server / Oracle / MS Access:

MySQL:

DROP a CHECK Constraint

To drop a CHECK constraint, use the following SQL:

ALTER TABLE Persons

DROP CONSTRAINT CHK_PersonAge;

ALTER TABLE Persons

DROP CHECK CHK_PersonAge;

SQL Server / Oracle / MS Access:

MySQL: