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Enhanced cycle mark values

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Per SQL:202x draft, in the CYCLE clause of a recursive query, the
cycle mark values can be of type boolean and can be omitted, in which
case they default to TRUE and FALSE.

Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Discussion: https://www.postgresql.org/message-id/flat/db80ceee-6f97-9b4a-8ee8-3ba0c58e5be2@2ndquadrant.com
This commit is contained in:
Peter Eisentraut
2021-02-27 08:11:14 +01:00
parent 4e90052c46
commit f4adc41c4f
7 changed files with 144 additions and 47 deletions
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5
doc/src/sgml/queries.sgml
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@@ -2349,14 +2349,13 @@ WITH RECURSIVE search_graph(id, link, data, depth) AS (
SELECT g.id, g.link, g.data, sg.depth + 1
FROM graph g, search_graph sg
WHERE g.id = sg.link
) <emphasis>CYCLE id SET is_cycle TO true DEFAULT false USING path</emphasis>
) <emphasis>CYCLE id SET is_cycle USING path</emphasis>
SELECT * FROM search_graph;
</programlisting>
and it will be internally rewritten to the above form. The
<literal>CYCLE</literal> clause specifies first the list of columns to
track for cycle detection, then a column name that will show whether a
cycle has been detected, then two values to use in that column for the yes
and no cases, and finally the name of another column that will track the
cycle has been detected, and finally the name of another column that will track the
path. The cycle and path columns will implicitly be added to the output
rows of the CTE.
</para>