COMMENT — define or change the comment of an object
COMMENT ON { TABLEobject_name
| COLUMNtable_name
.column_name
| AGGREGATEagg_name
(agg_type
) | CAST (sourcetype
AStargettype
) | CONSTRAINTconstraint_name
ONtable_name
| CONVERSIONobject_name
| DATABASEobject_name
| DOMAINobject_name
| FUNCTIONfunc_name
(arg1_type
,arg2_type
, ...) | INDEXobject_name
| LARGE OBJECTlarge_object_oid
| OPERATORop
(leftoperand_type
,rightoperand_type
) | OPERATOR CLASSobject_name
USINGindex_method
| [ PROCEDURAL ] LANGUAGEobject_name
| RULErule_name
ONtable_name
| SCHEMAobject_name
| SEQUENCEobject_name
| TRIGGERtrigger_name
ONtable_name
| TYPEobject_name
| VIEWobject_name
} IS'text'
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, “Comment Information Functions”).
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.
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.
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';