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>45.6. <TT
CLASS="STRUCTNAME"
>pg_attrdef</TT
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><P
>   The catalog <TT
CLASS="STRUCTNAME"
>pg_attrdef</TT
> stores column default values.  The main information
   about columns is stored in <TT
CLASS="STRUCTNAME"
>pg_attribute</TT
>
   (see below).  Only columns that explicitly specify a default value
   (when the table is created or the column is added) will have an
   entry here.
  </P
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>Table 45-6. <TT
CLASS="STRUCTNAME"
>pg_attrdef</TT
> Columns</B
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>Name</TH
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>Type</TH
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>References</TH
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>Description</TH
></TR
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><TR
><TD
><TT
CLASS="STRUCTFIELD"
>adrelid</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-class.html"
><TT
CLASS="STRUCTNAME"
>pg_class</TT
></A
>.oid</TT
></TD
><TD
>The table this column belongs to</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>adnum</TT
></TD
><TD
><TT
CLASS="TYPE"
>int2</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-attribute.html"
><TT
CLASS="STRUCTNAME"
>pg_attribute</TT
></A
>.attnum</TT
></TD
><TD
>The number of the column</TD
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><TT
CLASS="STRUCTFIELD"
>adbin</TT
></TD
><TD
><TT
CLASS="TYPE"
>pg_node_tree</TT
></TD
><TD
>&nbsp;</TD
><TD
>The internal representation of the column default value</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>adsrc</TT
></TD
><TD
><TT
CLASS="TYPE"
>text</TT
></TD
><TD
>&nbsp;</TD
><TD
>A human-readable representation of the default value</TD
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><P
>    The <TT
CLASS="STRUCTFIELD"
>adsrc</TT
> field is historical, and is best
    not used, because it does not track outside changes that might affect
    the representation of the default value.  Reverse-compiling the
    <TT
CLASS="STRUCTFIELD"
>adbin</TT
> field (with <CODE
CLASS="FUNCTION"
>pg_get_expr</CODE
> for
    example) is a better way to display the default value.
   </P
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