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COMMENT

Name

COMMENT -- define 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 |
  FUNCTION func_name (arg1_type, arg2_type, ...) |
  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 |
  RULE rule_name ON table_name |
  SCHEMA object_name |
  SEQUENCE 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 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 and col_description (see Table 9-43).

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.

agg_type

The argument data type of the aggregate function, or * if the function accepts any data type.

large_object_oid

The OID of the large object.

PROCEDURAL

This is a noise word.

sourcetype

The name of the source data type of the cast.

targettype

The name of the target data type of the cast.

text

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

Notes

A comment for a database can only be created in that database, and will only be visible in that database, not in other databases.

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 don't own). Therefore, don't 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;

Some more examples:

COMMENT ON AGGREGATE my_aggregate (double precision) IS 'Computes sample variance';
COMMENT ON CAST (text AS int4) IS 'Allow casts from text to int4';
COMMENT ON COLUMN my_table.my_column IS 'Employee ID number';
COMMENT ON CONVERSION my_conv IS 'Conversion to Unicode';
COMMENT ON DATABASE my_database IS 'Development Database';
COMMENT ON DOMAIN my_domain IS 'Email Address Domain';
COMMENT ON FUNCTION my_function (timestamp) IS 'Returns Roman Numeral';
COMMENT ON INDEX my_index IS 'Enforces uniqueness on employee ID';
COMMENT ON LANGUAGE plpython IS 'Python support for stored procedures';
COMMENT ON LARGE OBJECT 346344 IS 'Planning document';
COMMENT ON OPERATOR ^ (text, text) IS 'Performs intersection of two texts';
COMMENT ON OPERATOR ^ (NONE, text) IS 'This is a prefix operator on text';
COMMENT ON OPERATOR CLASS int4ops USING btree IS '4 byte integer operators for btrees';
COMMENT ON RULE my_rule ON my_table IS 'Logs updates of employee records';
COMMENT ON SCHEMA my_schema IS 'Departmental data';
COMMENT ON SEQUENCE my_sequence IS 'Used to generate primary keys';
COMMENT ON TABLE my_schema.my_table IS 'Employee Information';
COMMENT ON TRIGGER my_trigger ON my_table IS 'Used for RI';
COMMENT ON TYPE complex IS 'Complex number data type';
COMMENT ON VIEW my_view IS 'View of departmental costs';

Compatibility

There is no COMMENT command in the SQL standard.

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