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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:

SQL Server / Oracle / MS Access:

ALTER TABLE Persons
DROP CONSTRAINT UC_Person;

MySQL:

ALTER TABLE Persons
DROP INDEX UC_Person;

DROP a PRIMARY KEY Constraint

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

SQL Server / Oracle / MS Access:

ALTER TABLE Persons
DROP CONSTRAINT PK_Person;

MySQL:

ALTER TABLE Persons
DROP PRIMARY KEY;

DROP a FOREIGN KEY Constraint

To drop 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;

DROP a CHECK Constraint

To drop 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;

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