Defines or change the comment of an object.

Synopsis

COMMENT ON
{ TABLE <object_name> |
  COLUMN <table_name.column_name> |
  AGGREGATE <agg_name> (<agg_type> [, ...]) |
  CAST (<sourcetype> AS <targettype>) |
  CONSTRAINT <constraint_name> ON <table_name> |
  CONVERSION <object_name> |
  DATABASE <object_name> |
  DOMAIN <object_name> |
  FILESPACE <object_name> |
  FUNCTION <func_name> ([[<argmode>] [<argname>] <argtype> [, ...]]) |
  INDEX <object_name> |
  LARGE OBJECT <large_object_oid> |
  OPERATOR <op> (<leftoperand_type>, <rightoperand_type>) |
  OPERATOR CLASS <object_name> USING <index_method> |
  [PROCEDURAL] LANGUAGE <object_name> |
  RESOURCE QUEUE <object_name> |
  ROLE <object_name> |
  RULE <rule_name> ON <table_name> |
  SCHEMA <object_name> |
  SEQUENCE <object_name> |
  TABLESPACE <object_name> |
  TRIGGER <trigger_name> ON <table_name> |
  TYPE <object_name> |
  VIEW <object_name> } 
IS '<text>'

Description

COMMENT stores a comment about a database object. To modify a comment, issue a new COMMENT command for the same object. Only one comment string is stored for each object. To remove a comment, write NULL in place of the text string. Comments are automatically dropped when the object is dropped.

Comments can be easily retrieved with the psql meta-commands \dd, \d+, and \l+. Other user interfaces to retrieve comments can be built atop the same built-in functions that psql uses, namely obj_description, col_description, and shobj_description.

Parameters

object_name

table_name.column_name

agg_name

constraint_name

func_name

op

rule_name

trigger_name

The name of the object to be commented. Names of tables, aggregates, domains, functions, indexes, operators, operator classes, sequences, types, and views may be schema-qualified.

Note: Greenplum Database does not support triggers.

agg_type

An input data type on which the aggregate function operates. To reference a zero-argument aggregate function, write * in place of the list of input data types.

sourcetype

The name of the source data type of the cast.

targettype

The name of the target data type of the cast.

argmode

The mode of a function argument: either IN, OUT, INOUT, or VARIADIC. If omitted, the default is IN. Note that COMMENT ON FUNCTION does not actually pay any attention to OUT arguments, since only the input arguments are needed to determine the function's identity. So it is sufficient to list the IN, INOUT, and VARIADIC arguments.

argname

The name of a function argument. Note that COMMENT ON FUNCTION does not actually pay any attention to argument names, since only the argument data types are needed to determine the function's identity.

argtype

The data type(s) of the function's arguments (optionally schema-qualified), if any.

large_object_oid

The OID of the large object.

PROCEDURAL

This is a noise word.

text

The new comment, written as a string literal; or NULL to drop the comment.

Notes

There is presently no security mechanism for comments: any user connected to a database can see all the comments for objects in that database (although only superusers can change comments for objects that they do not own). For shared objects such as databases, roles, and tablespaces comments are stored globally and any user connected to any database can see all the comments for shared objects. Therefore, do not put security-critical information in comments.

Examples

Attach a comment to the table mytable:

COMMENT ON TABLE mytable IS 'This is my table.';

Remove it again:

COMMENT ON TABLE mytable IS NULL;

Compatibility

There is no COMMENT statement in the SQL standard.

Parent topic: SQL Command Reference