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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/comment.sgml,v 1.23 2003/09/09 18:28:52 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>
<indexterm zone="sql-comment">
<primary>COMMENT</primary>
</indexterm>
<refsynopsisdiv>
<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>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>COMMENT</command> stores a comment about a database object.
Comments can be
easily retrieved with the <application>psql</application> commands
<command>\dd</command>, <command>\d+</command>, and <command>\l+</command>.
Other user interfaces to retrieve comments can be built atop
the same built-in functions that <application>psql</application> 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>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="parameter">object_name</replaceable></term>
<term><replaceable class="parameter">table_name.column_name</replaceable></term>
<term><replaceable class="parameter">aggname</replaceable></term>
<term><replaceable class="parameter">constraint_name</replaceable></term>
<term><replaceable class="parameter">func_name</replaceable></term>
<term><replaceable class="parameter">op</replaceable></term>
<term><replaceable class="parameter">rule_name</replaceable></term>
<term><replaceable class="parameter">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 new comment.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<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>
</refsect1>
<refsect1>
<title>Examples</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_column 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 RI';
COMMENT ON TYPE complex IS 'Complex number data type';
COMMENT ON VIEW my_view IS 'View of departmental costs';
</programlisting>
</para>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
There is no <command>COMMENT</command> command in the SQL standard.
</para>
</refsect1>
</refentry>
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