PostgreSQL 8.2.3 Documentation
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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 |
      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 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` (see Table 9-44).

## 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`

  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`, 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

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). 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, 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 ROLE my_role IS 'Administration group for finance tables';
    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 TABLESPACE my_tablespace IS 'Tablespace for indexes';
    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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