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><H1
><A
NAME="SQL-COMMENT"
></A
>COMMENT</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN38043"
></A
><H2
>Name</H2
>COMMENT -- define or change the comment of an object</DIV
><A
NAME="AEN38046"
></A
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN38048"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>COMMENT ON
{
TABLE <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
COLUMN <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
>.<TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> |
AGGREGATE <TT
CLASS="REPLACEABLE"
><I
>agg_name</I
></TT
> (<TT
CLASS="REPLACEABLE"
><I
>agg_type</I
></TT
>) |
CAST (<TT
CLASS="REPLACEABLE"
><I
>sourcetype</I
></TT
> AS <TT
CLASS="REPLACEABLE"
><I
>targettype</I
></TT
>) |
CONSTRAINT <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
> ON <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
> |
CONVERSION <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
DATABASE <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
DOMAIN <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
FUNCTION <TT
CLASS="REPLACEABLE"
><I
>func_name</I
></TT
> (<TT
CLASS="REPLACEABLE"
><I
>arg1_type</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>arg2_type</I
></TT
>, ...) |
INDEX <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
LARGE OBJECT <TT
CLASS="REPLACEABLE"
><I
>large_object_oid</I
></TT
> |
OPERATOR <TT
CLASS="REPLACEABLE"
><I
>op</I
></TT
> (<TT
CLASS="REPLACEABLE"
><I
>leftoperand_type</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>rightoperand_type</I
></TT
>) |
OPERATOR CLASS <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> USING <TT
CLASS="REPLACEABLE"
><I
>index_method</I
></TT
> |
[ PROCEDURAL ] LANGUAGE <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
RULE <TT
CLASS="REPLACEABLE"
><I
>rule_name</I
></TT
> ON <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
> |
SCHEMA <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
SEQUENCE <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
TRIGGER <TT
CLASS="REPLACEABLE"
><I
>trigger_name</I
></TT
> ON <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
> |
TYPE <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
> |
VIEW <TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
>
} IS <TT
CLASS="REPLACEABLE"
><I
>'text'</I
></TT
></PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN38082"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>COMMENT</TT
> stores a comment about a database object.
</P
><P
> To modify a comment, issue a new <TT
CLASS="COMMAND"
>COMMENT</TT
> command for the
same object. Only one comment string is stored for each object.
To remove a comment, write <TT
CLASS="LITERAL"
>NULL</TT
> in place of the text
string.
Comments are automatically dropped when the object is dropped.
</P
><P
> Comments can be
easily retrieved with the <SPAN
CLASS="APPLICATION"
>psql</SPAN
> commands
<TT
CLASS="COMMAND"
>\dd</TT
>, <TT
CLASS="COMMAND"
>\d+</TT
>, and <TT
CLASS="COMMAND"
>\l+</TT
>.
Other user interfaces to retrieve comments can be built atop
the same built-in functions that <SPAN
CLASS="APPLICATION"
>psql</SPAN
> uses, namely
<CODE
CLASS="FUNCTION"
>obj_description</CODE
> and <CODE
CLASS="FUNCTION"
>col_description</CODE
>
(see <A
HREF="functions-info.html#FUNCTIONS-INFO-COMMENT-TABLE"
>Table 9-43</A
>).
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN38098"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="REPLACEABLE"
><I
>object_name</I
></TT
><BR><TT
CLASS="REPLACEABLE"
><I
>table_name.column_name</I
></TT
><BR><TT
CLASS="REPLACEABLE"
><I
>agg_name</I
></TT
><BR><TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
><BR><TT
CLASS="REPLACEABLE"
><I
>func_name</I
></TT
><BR><TT
CLASS="REPLACEABLE"
><I
>op</I
></TT
><BR><TT
CLASS="REPLACEABLE"
><I
>rule_name</I
></TT
><BR><TT
CLASS="REPLACEABLE"
><I
>trigger_name</I
></TT
></DT
><DD
><P
> 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.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>agg_type</I
></TT
></DT
><DD
><P
> The argument data type of the aggregate function, or
<TT
CLASS="LITERAL"
>*</TT
> if the function accepts any data type.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>large_object_oid</I
></TT
></DT
><DD
><P
> The OID of the large object.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>PROCEDURAL</TT
></DT
><DD
><P
> This is a noise word.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>sourcetype</I
></TT
></DT
><DD
><P
> The name of the source data type of the cast.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>targettype</I
></TT
></DT
><DD
><P
> The name of the target data type of the cast.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>text</I
></TT
></DT
><DD
><P
> The new comment, written as a string literal; or <TT
CLASS="LITERAL"
>NULL</TT
>
to drop the comment.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN38152"
></A
><H2
>Notes</H2
><P
> A comment for a database can only be created in that database,
and will only be visible in that database, not in other databases.
</P
><P
> 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.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN38156"
></A
><H2
>Examples</H2
><P
> Attach a comment to the table <TT
CLASS="LITERAL"
>mytable</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>COMMENT ON TABLE mytable IS 'This is my table.';</PRE
><P>
Remove it again:
</P><PRE
CLASS="PROGRAMLISTING"
>COMMENT ON TABLE mytable IS NULL;</PRE
><P>
</P
><P
> Some more examples:
</P><PRE
CLASS="PROGRAMLISTING"
>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';</PRE
><P>
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN38164"
></A
><H2
>Compatibility</H2
><P
> There is no <TT
CLASS="COMMAND"
>COMMENT</TT
> command in the SQL standard.
</P
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