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DROP CONSTRAINT clause

  • Artikkeli

Applies to: check marked yes Databricks SQL check marked yes Databricks Runtime

Drops a PRIMARY KEY, FOREIGN KEY, or CHECK constraint from the table.

Syntax

DROP { PRIMARY KEY [ IF EXISTS ] [ RESTRICT | CASCADE ] |
       FOREIGN KEY [ IF EXISTS ] ( column [, ...] ) |
       CONSTRAINT [ IF EXISTS ] name [ RESTRICT | CASCADE ] }

Parameters

  • PRIMARY KEY [ IF EXISTS ]

    Applies to: check marked yes Databricks SQL check marked yes Databricks Runtime 11.3 LTS and above check marked yes Unity Catalog only

    Drops the primary key from the table.

  • FOREIGN KEY [ IF EXISTS ] ( column [, …] )

    Applies to: check marked yes Databricks SQL check marked yes Databricks Runtime 11.3 LTS and above check marked yes Unity Catalog only

    Drops the foreign key identified by the ordered list of columns.

  • CONSTRAINT [ IF EXISTS ] name

    Drops the primary key, foreign key, or check constraint identified by name. Check constraints can only be dropped by name.

  • RESTRICT or CASCADE

    If you specify RESTRICT and the primary key is referenced by any foreign key, the statement will fail. If you specify CASCADE, dropping the primary key results in dropping any foreign keys referencing the table. The default is RESTRICT.

  • IF EXISTS

    If you specify IF EXISTS the statement will be ignored if the table has no matching constraint.

Examples

> CREATE TABLE persons(first_name STRING NOT NULL, last_name STRING NOT NULL, nickname STRING);
> ALTER TABLE persons ADD CONSTRAINT persons_pk PRIMARY KEY(first_name, last_name);

> CREATE TABLE pets(name STRING, owner_first_name STRING, owner_last_name STRING);
> ALTER TABLE pets ADD CONSTRAINT pets_persons_fk FOREIGN KEY (owner_first_name, owner_last_name) REFERENCES persons;

> ALTER TABLE pets ADD CONSTRAINT pets_name_not_cute_chk CHECK (length(name) < 20);

-- Drop the check constraint by name
> ALTER TABLE pets DROP CONSTRAINT pets_name_not_cute_chk;

-- Attempt to drop the primary key of persons by name
> ALTER TABLE persons DROP CONSTRAINT persons_pk RESTRICT;
  Error: A foreign key `pets_persons_fk` depends on the primary key

-- Drop the foreign key from pets by listing the columns
> ALTER TABLE pets DROP FOREIGN KEY IF EXISTS  (owner_first_name, owner_last_name);

-- Drop the primary key of persons
> ALTER TABLE persons DROP PRIMARY KEY CASCADE;