The DROP CONSTRAINT
statement is part of ALTER TABLE
and removes CHECK
and FOREIGN KEY
constraints from columns.
PRIMARY KEY
constraints can be dropped with DROP CONSTRAINT
if an ADD CONSTRAINT
statement follows the DROP CONSTRAINT
statement in the same transaction.
When you change a primary key with ALTER TABLE ... ALTER PRIMARY KEY
, the old primary key index becomes a secondary index. If you do not want the old primary key to become a secondary index, use DROP CONSTRAINT
/ADD CONSTRAINT
to change the primary key.
For information about removing other constraints, see Constraints: Remove Constraints.
This command can be combined with other ALTER TABLE
commands in a single statement. For a list of commands that can be combined, see ALTER TABLE
. For a demonstration, see Add and rename columns atomically.
Synopsis
Required privileges
The user must have the CREATE
privilege on the table.
Parameters
Parameter | Description |
---|---|
table_name |
The name of the table with the constraint you want to drop. |
name |
The name of the constraint you want to drop. |
Viewing schema changes
This schema change statement is registered as a job. You can view long-running jobs with SHOW JOBS
.
Examples
Setup
The following examples use MovR, a fictional vehicle-sharing application, to demonstrate CockroachDB SQL statements. For more information about the MovR example application and dataset, see MovR: A Global Vehicle-sharing App.
To follow along, run cockroach demo
to start a temporary, in-memory cluster with the movr
dataset preloaded:
$ cockroach demo
Drop a foreign key constraint
> SHOW CONSTRAINTS FROM vehicles;
table_name | constraint_name | constraint_type | details | validated
-------------+-------------------+-----------------+---------------------------------------------------------+------------
vehicles | fk_city_ref_users | FOREIGN KEY | FOREIGN KEY (city, owner_id) REFERENCES users(city, id) | true
vehicles | primary | PRIMARY KEY | PRIMARY KEY (city ASC, id ASC) | true
(2 rows)
> ALTER TABLE vehicles DROP CONSTRAINT fk_city_ref_users;
> SHOW CONSTRAINTS FROM vehicles;
table_name | constraint_name | constraint_type | details | validated
-------------+-----------------+-----------------+--------------------------------+------------
vehicles | primary | PRIMARY KEY | PRIMARY KEY (city ASC, id ASC) | true
(1 row)
Drop and add a primary key constraint
When you change a primary key with ALTER TABLE ... ALTER PRIMARY KEY
, the old primary key index becomes a secondary index. If you do not want the old primary key to become a secondary index when changing a primary key, you can use DROP CONSTRAINT
/ADD CONSTRAINT
instead.
Suppose that you want to add name
to the composite primary key of the users
table.
> SHOW CREATE TABLE users;
table_name | create_statement
-------------+--------------------------------------------------------------
users | CREATE TABLE users (
| id UUID NOT NULL,
| city VARCHAR NOT NULL,
| name VARCHAR NULL,
| address VARCHAR NULL,
| credit_card VARCHAR NULL,
| CONSTRAINT "primary" PRIMARY KEY (city ASC, id ASC),
| FAMILY "primary" (id, city, name, address, credit_card)
| )
(1 row)
First, add a NOT NULL
constraint to the name
column with ALTER COLUMN
.
> ALTER TABLE users ALTER COLUMN name SET NOT NULL;
Then, in the same transaction, DROP
the old "primary"
constraint and ADD
the new one:
> BEGIN;
> ALTER TABLE users DROP CONSTRAINT "primary";
> ALTER TABLE users ADD CONSTRAINT "primary" PRIMARY KEY (city, name, id);
> COMMIT;
NOTICE: primary key changes are finalized asynchronously; further schema changes on this table may be restricted until the job completes
> SHOW CREATE TABLE users;
table_name | create_statement
-------------+---------------------------------------------------------------------
users | CREATE TABLE users (
| id UUID NOT NULL,
| city VARCHAR NOT NULL,
| name VARCHAR NOT NULL,
| address VARCHAR NULL,
| credit_card VARCHAR NULL,
| CONSTRAINT "primary" PRIMARY KEY (city ASC, name ASC, id ASC),
| FAMILY "primary" (id, city, name, address, credit_card)
| )
(1 row)
Using ALTER PRIMARY KEY
would have created a UNIQUE
secondary index called users_city_id_key
. Instead, there is just one index for the primary key constraint.