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NAME="CATALOG-PG-ENUM"
>45.20. <TT
CLASS="STRUCTNAME"
>pg_enum</TT
></A
></H1
><P
>   The <TT
CLASS="STRUCTNAME"
>pg_enum</TT
> catalog contains entries
   showing the values and labels for each enum type. The
   internal representation of a given enum value is actually the OID
   of its associated row in <TT
CLASS="STRUCTNAME"
>pg_enum</TT
>.
  </P
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>Table 45-20. <TT
CLASS="STRUCTNAME"
>pg_enum</TT
> Columns</B
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><TH
>Name</TH
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>Type</TH
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>References</TH
><TH
>Description</TH
></TR
></THEAD
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><TR
><TD
><TT
CLASS="STRUCTFIELD"
>enumtypid</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-type.html"
><TT
CLASS="STRUCTNAME"
>pg_type</TT
></A
>.oid</TT
></TD
><TD
>The OID of the <TT
CLASS="STRUCTNAME"
>pg_type</TT
> entry owning this enum value</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>enumsortorder</TT
></TD
><TD
><TT
CLASS="TYPE"
>float4</TT
></TD
><TD
>&nbsp;</TD
><TD
>The sort position of this enum value within its enum type</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>enumlabel</TT
></TD
><TD
><TT
CLASS="TYPE"
>name</TT
></TD
><TD
>&nbsp;</TD
><TD
>The textual label for this enum value</TD
></TR
></TBODY
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><P
>   The OIDs for <TT
CLASS="STRUCTNAME"
>pg_enum</TT
> rows follow a special
   rule: even-numbered OIDs are guaranteed to be ordered in the same way
   as the sort ordering of their enum type.  That is, if two even OIDs
   belong to the same enum type, the smaller OID must have the smaller
   <TT
CLASS="STRUCTFIELD"
>enumsortorder</TT
> value.  Odd-numbered OID values
   need bear no relationship to the sort order.  This rule allows the
   enum comparison routines to avoid catalog lookups in many common cases.
   The routines that create and alter enum types attempt to assign even
   OIDs to enum values whenever possible.
  </P
><P
>   When an enum type is created, its members are assigned sort-order
   positions 1..<TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
>.  But members added later might be given
   negative or fractional values of <TT
CLASS="STRUCTFIELD"
>enumsortorder</TT
>.
   The only requirement on these values is that they be correctly
   ordered and unique within each enum type.
  </P
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