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The COMMENT ON statement associates comments to databases, tables, columns, or indexes.
Required privileges
The user must have the CREATE privilege on the object they are commenting on.
Synopsis
Parameters
| Parameter | Description |
|---|---|
database_name |
The name of the database on which you are commenting. |
table_name |
The name of the table on which you are commenting. |
column_name |
The name of the column on which you are commenting. |
table_index_name |
The name of the index on which you are commenting. |
comment_text |
The comment (STRING) you are associating to the object. You can remove a comment by replacing the string with NULL. |
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
Add a comment to a database
To add a comment to a database:
> COMMENT ON DATABASE movr IS 'This database contains information about users, vehicles, and rides.';
To view database comments, use SHOW DATABASES:
> SHOW DATABASES WITH COMMENT;
database_name | owner | primary_region | regions | survival_goal | comment
----------------+-------+----------------+---------+---------------+-----------------------------------------------------------------------
defaultdb | root | NULL | {} | NULL | NULL
movr | demo | NULL | {} | NULL | This database contains information about users, vehicles, and rides.
postgres | root | NULL | {} | NULL | NULL
system | node | NULL | {} | NULL | NULL
(4 rows)
Add a comment to a table
To add a comment to a table:
> COMMENT ON TABLE vehicles IS 'This table contains information about vehicles registered with MovR.';
To view table comments, use SHOW TABLES:
> SHOW TABLES FROM movr WITH COMMENT;
table_name | comment
+----------------------------+----------------------------------------------------------------------+
users |
vehicles | This table contains information about vehicles registered with MovR.
rides |
vehicle_location_histories |
promo_codes |
user_promo_codes |
(6 rows)
You can also view comments on a table with SHOW CREATE:
> SHOW CREATE TABLE vehicles;
table_name | create_statement
-------------+------------------------------------------------------------------------------------------------------
vehicles | CREATE TABLE vehicles (
| id UUID NOT NULL,
| city VARCHAR NOT NULL,
| type VARCHAR NULL,
| owner_id UUID NULL,
| creation_time TIMESTAMP NULL,
| status VARCHAR NULL,
| current_location VARCHAR NULL,
| ext JSONB NULL,
| CONSTRAINT "primary" PRIMARY KEY (city ASC, id ASC),
| CONSTRAINT fk_city_ref_users FOREIGN KEY (city, owner_id) REFERENCES users(city, id),
| INDEX vehicles_auto_index_fk_city_ref_users (city ASC, owner_id ASC),
| FAMILY "primary" (id, city, type, owner_id, creation_time, status, current_location, ext)
| );
| COMMENT ON TABLE vehicles IS 'This table contains information about vehicles registered with MovR.'
(1 row)
Add a comment to a column
To add a comment to a column:
> COMMENT ON COLUMN users.credit_card IS 'This column contains user payment information.';
To view column comments, use SHOW COLUMNS:
> SHOW COLUMNS FROM users WITH COMMENT;
column_name | data_type | is_nullable | column_default | generation_expression | indices | is_hidden | comment
+-------------+-----------+-------------+----------------+-----------------------+-----------+-----------+------------------------------------------------+
id | UUID | false | NULL | | {primary} | false | NULL
city | VARCHAR | false | NULL | | {primary} | false | NULL
name | VARCHAR | true | NULL | | {} | false | NULL
address | VARCHAR | true | NULL | | {} | false | NULL
credit_card | VARCHAR | true | NULL | | {} | false | This column contains user payment information.
(5 rows)
Add a comment to an index
Suppose we create an index on the name column of the users table:
> CREATE INDEX ON users(name);
To add a comment to the index:
> COMMENT ON INDEX users_name_idx IS 'This index improves performance on queries that filter by name.';
To view column comments, use SHOW INDEXES ... WITH COMMENT:
> SHOW INDEXES FROM users WITH COMMENT;
table_name | index_name | non_unique | seq_in_index | column_name | direction | storing | implicit | comment
-------------+----------------+------------+--------------+-------------+-----------+---------+----------+------------------------------------------------------------------
users | primary | false | 1 | city | ASC | false | false | NULL
users | primary | false | 2 | id | ASC | false | false | NULL
users | users_name_idx | true | 1 | name | ASC | false | false | This index improves performance on queries that filter by name.
users | users_name_idx | true | 2 | city | ASC | false | true | This index improves performance on queries that filter by name.
users | users_name_idx | true | 3 | id | ASC | false | true | This index improves performance on queries that filter by name.
users | primary | false | 1 | city | ASC | false | false | NULL
users | primary | false | 2 | id | ASC | false | false | NULL
...
(15 rows)
Remove a comment from a database
To remove a comment from a database:
> COMMENT ON DATABASE movr IS NULL;
> SHOW DATABASES WITH COMMENT;
database_name | owner | primary_region | regions | survival_goal | comment
----------------+-------+----------------+---------+---------------+----------
defaultdb | root | NULL | {} | NULL | NULL
movr | demo | NULL | {} | NULL | NULL
postgres | root | NULL | {} | NULL | NULL
system | node | NULL | {} | NULL | NULL
(4 rows)
