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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/comment.sgml,v 1.20 2002/07/12 18:43:12 tgl Exp $
PostgreSQL documentation
-->
<refentry id="SQL-COMMENT">
<refmeta>
<refentrytitle id="SQL-COMMENT-TITLE">COMMENT</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>
COMMENT
</refname>
<refpurpose>
define or change the comment of an object
</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
<date>1999-07-20</date>
</refsynopsisdivinfo>
<synopsis>
COMMENT ON
[
TABLE <replaceable class="PARAMETER">object_name</replaceable> |
COLUMN <replaceable class="PARAMETER">table_name</replaceable>.<replaceable class="PARAMETER">column_name</replaceable> |
AGGREGATE <replaceable class="PARAMETER">agg_name</replaceable> (<replaceable class="PARAMETER">agg_type</replaceable>) |
CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ON <replaceable class="PARAMETER">table_name</replaceable> |
DATABASE <replaceable class="PARAMETER">object_name</replaceable> |
DOMAIN <replaceable class="PARAMETER">object_name</replaceable> |
FUNCTION <replaceable class="PARAMETER">func_name</replaceable> (<replaceable class="PARAMETER">arg1_type</replaceable>, <replaceable class="PARAMETER">arg2_type</replaceable>, ...) |
INDEX <replaceable class="PARAMETER">object_name</replaceable> |
OPERATOR <replaceable class="PARAMETER">op</replaceable> (<replaceable class="PARAMETER">leftoperand_type</replaceable>, <replaceable class="PARAMETER">rightoperand_type</replaceable>) |
RULE <replaceable class="PARAMETER">rule_name</replaceable> ON <replaceable class="PARAMETER">table_name</replaceable> |
SCHEMA <replaceable class="PARAMETER">object_name</replaceable> |
SEQUENCE <replaceable class="PARAMETER">object_name</replaceable> |
TRIGGER <replaceable class="PARAMETER">trigger_name</replaceable> ON <replaceable class="PARAMETER">table_name</replaceable> |
TYPE <replaceable class="PARAMETER">object_name</replaceable> |
VIEW <replaceable class="PARAMETER">object_name</replaceable>
] IS <replaceable class="PARAMETER">'text'</replaceable>
</synopsis>
<refsect2 id="R2-SQL-COMMENT-1">
<refsect2info>
<date>1999-10-25</date>
</refsect2info>
<title>
Inputs
</title>
<para>
<variablelist>
<varlistentry>
<term><replaceable class="PARAMETER">object_name,
table_name.column_name, agg_name, constraint_name, func_name, op, rule_name, trigger_name</replaceable></term>
<listitem>
<para>
The name of the object to be be commented. Names of tables,
aggregates, domains, functions, indexes, operators, sequences, types,
and views
may be schema-qualified.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">text</replaceable></term>
<listitem>
<para>
The comment to add.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
<refsect2 id="R2-SQL-COMMENT-2">
<refsect2info>
<date>1998-09-08</date>
</refsect2info>
<title>
Outputs
</title>
<para>
<variablelist>
<varlistentry>
<term><computeroutput>
COMMENT
</computeroutput></term>
<listitem>
<para>
Message returned if the table is successfully commented.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
</refsynopsisdiv>
<refsect1 id="R1-SQL-COMMENT-1">
<refsect1info>
<date>1998-10-25</date>
</refsect1info>
<title>
Description
</title>
<para>
<command>COMMENT</command> stores a comment about a database object.
Comments can be
easily retrieved with <command>psql</command>'s
<command>\dd</command>, <command>\d+</command>, or <command>\l+</command>
commands. Other user interfaces to retrieve comments can be built atop
the same built-in functions that <command>psql</command> uses, namely
<function>obj_description()</> and <function>col_description()</>.
</para>
<para>
To modify a comment, issue a new <command>COMMENT</> command for the
same object. Only one comment string is stored for each object.
To remove a comment, write <literal>NULL</literal> in place of the text
string.
Comments are automatically dropped when the object is dropped.
</para>
<note>
<para>
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.
</para>
</note>
</refsect1>
<refsect1 id="R1-SQL-COMMENT-2">
<title>
Usage
</title>
<para>
Attach a comment to the table <literal>mytable</literal>:
<programlisting>
COMMENT ON TABLE mytable IS 'This is my table.';
</programlisting>
Remove it again:
<programlisting>
COMMENT ON TABLE mytable IS NULL;
</programlisting>
</para>
<para>
Some more examples:
<programlisting>
COMMENT ON AGGREGATE my_aggregate (double precision) IS 'Computes sample variance';
COMMENT ON COLUMN my_table.my_field IS 'Employee ID number';
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 OPERATOR ^ (text, text) IS 'Performs intersection of two texts';
COMMENT ON OPERATOR ^ (NONE, text) IS 'This is a prefix operator on text';
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 R.I.';
COMMENT ON TYPE complex IS 'Complex Number datatype';
COMMENT ON VIEW my_view IS 'View of departmental costs';
</programlisting>
</para>
</refsect1>
<refsect1 id="R1-SQL-COMMENT-3">
<title>
Compatibility
</title>
<refsect2 id="R2-SQL-COMMENT-4">
<refsect2info>
<date>1998-09-08</date>
</refsect2info>
<title>
SQL92
</title>
<para>
There is no <command>COMMENT</command> in <acronym>SQL92</acronym>.
</para>
</refsect2>
</refsect1>
</refentry>
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