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
( [ [argmode
] [argname
]argtype
[, ...] ] ) | INDEXobject_name
| LARGE OBJECTlarge_object_oid
| OPERATORop
(leftoperand_type
,rightoperand_type
) | OPERATOR CLASSobject_name
USINGindex_method
| [ PROCEDURAL ] LANGUAGEobject_name
| ROLEobject_name
| RULErule_name
ONtable_name
| SCHEMAobject_name
| SEQUENCEobject_name
| TABLESPACEobject_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
, col_description
,
and shobj_description
(see Table 9.44, “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
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.
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.
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';