The DROP INDEX statement removes indexes from tables.
The DROP INDEX statement performs a schema change. For more information about how online schema changes work in CockroachDB, see Online Schema Changes.
Synopsis
Required privileges
The user must have the CREATE privilege on each specified table.
Parameters
| Parameter | Description |
|---|---|
IF EXISTS |
Drop the named indexes if they exist; if they do not exist, do not return an error. |
table_name |
The name of the table with the index you want to drop. Find table names with SHOW TABLES. |
index_name |
The name of the index you want to drop. Find index names with SHOW INDEX.You cannot drop a table's primary index. |
CASCADE |
Drop all objects (such as constraints) that depend on the indexes. CASCADE does not list objects it drops, so should be used cautiously.To drop an index created with CREATE UNIQUE INDEX, you do not need to use CASCADE. |
RESTRICT |
(Default) Do not drop the indexes if any objects (such as constraints) depend on them. |
CONCURRENTLY |
Optional, no-op syntax for PostgreSQL compatibility. All indexes are dropped concurrently in CockroachDB. |
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
Remove an index with no dependencies
UNIQUE indexes created as part of a CREATE TABLE statement cannot be removed without using CASCADE. Unique indexes created with CREATE INDEX do not have this limitation.
Suppose you create an index on the name and city columns of the users table:
> CREATE INDEX ON users (name, city);
> SHOW INDEXES FROM users;
table_name | index_name | non_unique | seq_in_index | column_name | direction | storing | implicit
-------------+---------------------+------------+--------------+-------------+-----------+---------+-----------
users | users_pkey | false | 1 | city | ASC | false | false
users | users_pkey | false | 2 | id | ASC | false | false
users | users_pkey | false | 3 | name | N/A | true | false
users | users_pkey | false | 4 | address | N/A | true | false
users | users_pkey | false | 5 | credit_card | N/A | true | false
users | users_name_city_idx | true | 1 | name | ASC | false | false
users | users_name_city_idx | true | 2 | city | ASC | false | false
users | users_name_city_idx | true | 3 | id | ASC | false | true
(8 rows)
You can drop this index with the DROP INDEX statement:
> DROP INDEX users@users_name_city_idx;
> SHOW INDEXES FROM users;
table_name | index_name | non_unique | seq_in_index | column_name | direction | storing | implicit
-------------+------------+------------+--------------+-------------+-----------+---------+-----------
users | users_pkey | false | 1 | city | ASC | false | false
users | users_pkey | false | 2 | id | ASC | false | false
users | users_pkey | false | 3 | name | N/A | true | false
users | users_pkey | false | 4 | address | N/A | true | false
users | users_pkey | false | 5 | credit_card | N/A | true | false
(5 rows)
Remove an index and dependent objects with CASCADE
CASCADE drops all dependent objects without listing them, which can lead to inadvertent and difficult-to-recover losses. To avoid potential harm, we recommend dropping objects individually in most cases.
Suppose you create a UNIQUE constraint on the id and name columns of the users table:
> ALTER TABLE users ADD CONSTRAINT id_name_unique UNIQUE (id, name);
> SHOW CONSTRAINTS from users;
table_name | constraint_name | constraint_type | details | validated
-------------+-----------------+-----------------+--------------------------------+------------
users | id_name_unique | false | 1 | id | ASC | false | false
users | id_name_unique | false | 2 | name | ASC | false | false
users | id_name_unique | false | 3 | city | ASC | false | true
users | users_pkey | false | 1 | city | ASC | false | false
users | users_pkey | false | 2 | id | ASC | false | false
users | users_pkey | false | 3 | name | N/A | true | false
users | users_pkey | false | 4 | address | N/A | true | false
users | users_pkey | false | 5 | credit_card | N/A | true | false
(8 rows)
If no index exists on id and name, CockroachDB automatically creates an index:
> SHOW INDEXES from users;
table_name | index_name | non_unique | seq_in_index | column_name | direction | storing | implicit
-------------+----------------+------------+--------------+-------------+-----------+---------+-----------
users | users_pkey | false | 1 | city | ASC | false | false
users | users_pkey | false | 2 | id | ASC | false | false
users | id_name_unique | false | 1 | id | ASC | false | false
users | id_name_unique | false | 2 | name | ASC | false | false
users | id_name_unique | false | 3 | city | ASC | false | true
(5 rows)
The UNIQUE constraint is dependent on the id_name_unique index, so you cannot drop the index with a simple DROP INDEX statement:
> DROP INDEX id_name_unique;
ERROR: index "id_name_unique" is in use as unique constraint
SQLSTATE: 2BP01
HINT: use CASCADE if you really want to drop it.
To drop an index and its dependent objects, you can use CASCADE:
> DROP INDEX id_name_unique CASCADE;
> SHOW INDEXES from users;
table_name | index_name | non_unique | seq_in_index | column_name | direction | storing | implicit
-------------+------------+------------+--------------+-------------+-----------+---------+-----------
users | users_pkey | false | 1 | city | ASC | false | false
users | users_pkey | false | 2 | id | ASC | false | false
users | users_pkey | false | 3 | name | N/A | true | false
users | users_pkey | false | 4 | address | N/A | true | false
users | users_pkey | false | 5 | credit_card | N/A | true | false
(5 rows)
> SHOW CONSTRAINTS from users;
table_name | constraint_name | constraint_type | details | validated
-------------+-----------------+-----------------+--------------------------------+------------
users | users_pkey | PRIMARY KEY | PRIMARY KEY (city ASC, id ASC) | true
(1 row)
See also
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