</para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conbin</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       If a check constraint, an internal representation of the
       expression.  (It's recommended to use
       <function>pg_get_constraintdef()</function> to extract the definition of
       a check constraint.)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   In the case of an exclusion constraint, <structfield>conkey</structfield>
   is only useful for constraint elements that are simple column references.
   For other cases, a zero appears in <structfield>conkey</structfield>
   and the associated index must be consulted to discover the expression
   that is constrained.  (<structfield>conkey</structfield> thus has the
   same contents as <link linkend="catalog-pg-index"><structname>pg_index</structname></link>.<structfield>indkey</structfield> for the
   index.)
  </para>

  <note>
   <para>
    <literal>pg_class.relchecks</literal> needs to agree with the
    number of check-constraint entries found in this table for each
    relation.
   </para>
  </note>
 </sect1>


 <sect1 id="catalog-pg-conversion">
  <title><structname>pg_conversion</structname></title>

  <indexterm zone="catalog-pg-conversion">
   <primary>pg_conversion</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_conversion</structname> describes
   encoding conversion functions.  See <xref linkend="sql-createconversion"/>
   for more information.
  </para>

  <table>
   <title><structname>pg_conversion</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conname</structfield> <type>name</type>
      </para>
      <para>
       Conversion name (unique within a namespace)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>connamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this conversion
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the conversion
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conforencoding</structfield> <type>int4</type>
      </para>
      <para>
       Source encoding ID (<link linkend="pg-encoding-to-char"><function>pg_encoding_to_char()</function></link>
       can translate this number to the encoding name)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>contoencoding</structfield> <type>int4</type>
      </para>
      <para>
       Destination encoding ID (<link linkend="pg-encoding-to-char"><function>pg_encoding_to_char()</function></link>
       can translate this number to the encoding name)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">