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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 ( [ [ 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 |
  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.

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, or INOUT. 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 and INOUT 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

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 UTF8';
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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