Sophie: postgresql8.3-docs-8.3.6-2mdv2008.1 x86

postgresql8.3-docs-8.3.6-2mdv2008.1.x86_64.rpm

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>intagg</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 8.3.6 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="Additional Supplied Modules"
HREF="contrib.html"><LINK
REL="PREVIOUS"
TITLE="hstore"
HREF="hstore.html"><LINK
REL="NEXT"
TITLE="intarray"
HREF="intarray.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2009-02-03T04:34:16"></HEAD
><BODY
CLASS="SECT1"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
>PostgreSQL 8.3.6 Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="hstore.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="contrib.html"
>Fast Backward</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Appendix F. Additional Supplied Modules</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="contrib.html"
>Fast Forward</A
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="intarray.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="INTAGG"
>F.11. intagg</A
></H1
><A
NAME="AEN100699"
></A
><P
>  The <TT
CLASS="FILENAME"
>intagg</TT
> module provides an integer aggregator and an
  enumerator.
 </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN100703"
>F.11.1. Functions</A
></H2
><P
>  The aggregator is an aggregate function
  <CODE
CLASS="FUNCTION"
>int_array_aggregate(integer)</CODE
>
  that produces an integer array
  containing exactly the integers it is fed.
  Here is a not-tremendously-useful example:
 </P
><PRE
CLASS="PROGRAMLISTING"
>test=# select int_array_aggregate(i) from
test-#   generate_series(1,10,2) i;
 int_array_aggregate
---------------------
 {1,3,5,7,9}
(1 row)
 </PRE
><P
>  The enumerator is a function
  <CODE
CLASS="FUNCTION"
>int_array_enum(integer[])</CODE
>
  that returns <TT
CLASS="TYPE"
>setof integer</TT
>.  It is essentially the reverse
  operation of the aggregator: given an array of integers, expand it
  into a set of rows.  For example,
 </P
><PRE
CLASS="PROGRAMLISTING"
>test=# select * from int_array_enum(array[1,3,5,7,9]);
 int_array_enum
----------------
              1
              3
              5
              7
              9
(5 rows)
 </PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN100712"
>F.11.2. Sample Uses</A
></H2
><P
>   Many database systems have the notion of a one to many table. Such a table
   usually sits between two indexed tables, for example:
  </P
><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE left (id INT PRIMARY KEY, ...);
CREATE TABLE right (id INT PRIMARY KEY, ...);
CREATE TABLE one_to_many(left INT REFERENCES left, right INT REFERENCES right);
 </PRE
><P
>  It is typically used like this:
 </P
><PRE
CLASS="PROGRAMLISTING"
>  SELECT right.* from right JOIN one_to_many ON (right.id = one_to_many.right)
    WHERE one_to_many.left = <TT
CLASS="REPLACEABLE"
><I
>item</I
></TT
>;
 </PRE
><P
>  This will return all the items in the right hand table for an entry
  in the left hand table. This is a very common construct in SQL.
 </P
><P
>  Now, this methodology can be cumbersome with a very large number of
  entries in the <TT
CLASS="STRUCTNAME"
>one_to_many</TT
> table.  Often,
  a join like this would result in an index scan
  and a fetch for each right hand entry in the table for a particular
  left hand entry. If you have a very dynamic system, there is not much you
  can do. However, if you have some data which is fairly static, you can
  create a summary table with the aggregator.
 </P
><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE summary as
  SELECT left, int_array_aggregate(right) AS right
  FROM one_to_many
  GROUP BY left;
 </PRE
><P
>  This will create a table with one row per left item, and an array
  of right items. Now this is pretty useless without some way of using
  the array; that's why there is an array enumerator.  You can do
 </P
><PRE
CLASS="PROGRAMLISTING"
>SELECT left, int_array_enum(right) FROM summary WHERE left = <TT
CLASS="REPLACEABLE"
><I
>item</I
></TT
>;
 </PRE
><P
>  The above query using <CODE
CLASS="FUNCTION"
>int_array_enum</CODE
> produces the same results
  as
 </P
><PRE
CLASS="PROGRAMLISTING"
>SELECT left, right FROM one_to_many WHERE left = <TT
CLASS="REPLACEABLE"
><I
>item</I
></TT
>;
 </PRE
><P
>  The difference is that the query against the summary table has to get
  only one row from the table, whereas the direct query against
  <TT
CLASS="STRUCTNAME"
>one_to_many</TT
> must index scan and fetch a row for each entry.
 </P
><P
>  On one system, an <TT
CLASS="COMMAND"
>EXPLAIN</TT
> showed a query with a cost of 8488 was
  reduced to a cost of 329.  The original query was a join involving the
  <TT
CLASS="STRUCTNAME"
>one_to_many</TT
> table, which was replaced by:
 </P
><PRE
CLASS="PROGRAMLISTING"
>SELECT right, count(right) FROM
  ( SELECT left, int_array_enum(right) AS right
    FROM summary JOIN (SELECT left FROM left_table WHERE left = <TT
CLASS="REPLACEABLE"
><I
>item</I
></TT
>) AS lefts
         ON (summary.left = lefts.left)
  ) AS list
  GROUP BY right
  ORDER BY count DESC;
 </PRE
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="hstore.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="intarray.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>hstore</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="contrib.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>intarray</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>