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Extend CTE patch to support recursive UNION (ie, without ALL). The

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implementation uses an in-memory hash table, so it will poop out for very
large recursive results ... but the performance characteristics of a
sort-based implementation would be pretty unpleasant too.
This commit is contained in:
Tom Lane
2008-10-07 19:27:04 +00:00
parent 059349be0c
commit 0d115dde82
13 changed files with 345 additions and 74 deletions
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8
doc/src/sgml/ref/select.sgml
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@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.105 2008/10/04 21:56:52 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.106 2008/10/07 19:27:04 tgl Exp $
PostgreSQL documentation
-->
@@ -202,10 +202,10 @@ and <replaceable class="parameter">with_query</replaceable> is:
subquery to reference itself by name. Such a subquery must have
the form
<synopsis>
<replaceable class="parameter">non_recursive_term</replaceable> UNION ALL <replaceable class="parameter">recursive_term</replaceable>
<replaceable class="parameter">non_recursive_term</replaceable> UNION [ ALL ] <replaceable class="parameter">recursive_term</replaceable>
</synopsis>
where the recursive self-reference must appear on the right-hand
side of <literal>UNION ALL</>. Only one recursive self-reference
side of the <literal>UNION</>. Only one recursive self-reference
is permitted per query.
</para>
@@ -1234,7 +1234,7 @@ SELECT distance, employee_name FROM employee_recursive;
</programlisting>
Notice the typical form of recursive queries:
an initial condition, followed by <literal>UNION ALL</literal>,
an initial condition, followed by <literal>UNION</literal>,
followed by the recursive part of the query. Be sure that the
recursive part of the query will eventually return no tuples, or
else the query will loop indefinitely. (See <xref linkend="queries-with">