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<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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