doc/src/sgml/func/func-enum.sgml - master - balmaster/postgres

doc/src/sgml/func/func-enum.sgml
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Andrew Dunstan
Split func.sgml into more manageable pieces
04 авг 2025, 16:04
04 авг 2025, 16:044e23c9e
 <sect1 id="functions-enum">
  <title>Enum Support Functions</title>

  <para>
   For enum types (described in <xref linkend="datatype-enum"/>),
   there are several functions that allow cleaner programming without
   hard-coding particular values of an enum type.
   These are listed in <xref linkend="functions-enum-table"/>. The examples
   assume an enum type created as:

<programlisting>
CREATE TYPE rainbow AS ENUM ('red', 'orange', 'yellow', 'green', 'blue', 'purple');
</programlisting>

  </para>

  <table id="functions-enum-table">
    <title>Enum Support Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para>
       <para>
        Example(s)
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>enum_first</primary>
        </indexterm>
        <function>enum_first</function> ( <type>anyenum</type> )
        <returnvalue>anyenum</returnvalue>
       </para>
       <para>
        Returns the first value of the input enum type.
       </para>
       <para>
        <literal>enum_first(null::rainbow)</literal>
        <returnvalue>red</returnvalue>
       </para></entry>
      </row>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>enum_last</primary>
        </indexterm>
        <function>enum_last</function> ( <type>anyenum</type> )
        <returnvalue>anyenum</returnvalue>
       </para>
       <para>
        Returns the last value of the input enum type.
       </para>
       <para>
        <literal>enum_last(null::rainbow)</literal>
        <returnvalue>purple</returnvalue>
       </para></entry>
      </row>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>enum_range</primary>
        </indexterm>
        <function>enum_range</function> ( <type>anyenum</type> )
        <returnvalue>anyarray</returnvalue>
       </para>
       <para>
        Returns all values of the input enum type in an ordered array.
       </para>
       <para>
        <literal>enum_range(null::rainbow)</literal>
        <returnvalue>{red,orange,yellow,&zwsp;green,blue,purple}</returnvalue>
       </para></entry>
      </row>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>enum_range</function> ( <type>anyenum</type>, <type>anyenum</type> )
        <returnvalue>anyarray</returnvalue>
       </para>
       <para>
        Returns the range between the two given enum values, as an ordered
        array. The values must be from the same enum type. If the first
        parameter is null, the result will start with the first value of
        the enum type.
        If the second parameter is null, the result will end with the last
        value of the enum type.
       </para>
       <para>
        <literal>enum_range('orange'::rainbow, 'green'::rainbow)</literal>
        <returnvalue>{orange,yellow,green}</returnvalue>
       </para>
       <para>
        <literal>enum_range(NULL, 'green'::rainbow)</literal>
        <returnvalue>{red,orange,&zwsp;yellow,green}</returnvalue>
       </para>
       <para>
        <literal>enum_range('orange'::rainbow, NULL)</literal>
        <returnvalue>{orange,yellow,green,&zwsp;blue,purple}</returnvalue>
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <para>
    Notice that except for the two-argument form of <function>enum_range</function>,
    these functions disregard the specific value passed to them; they care
    only about its declared data type.  Either null or a specific value of
    the type can be passed, with the same result.  It is more common to
    apply these functions to a table column or function argument than to
    a hardwired type name as used in the examples.
   </para>
 </sect1>