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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>

8
doc/src/sgml/ref/select.sgml
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@ -74,7 +74,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
<replaceable class="parameter">with_query_name</replaceable> [ ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ] AS [ [ NOT ] MATERIALIZED ] ( <replaceable class="parameter">select</replaceable> | <replaceable class="parameter">values</replaceable> | <replaceable class="parameter">insert</replaceable> | <replaceable class="parameter">update</replaceable> | <replaceable class="parameter">delete</replaceable> )
[ SEARCH { BREADTH | DEPTH } FIRST BY <replaceable>column_name</replaceable> [, ...] SET <replaceable>search_seq_col_name</replaceable> ]
[ CYCLE <replaceable>column_name</replaceable> [, ...] SET <replaceable>cycle_mark_col_name</replaceable> TO <replaceable>cycle_mark_value</replaceable> DEFAULT <replaceable>cycle_mark_default</replaceable> USING <replaceable>cycle_path_col_name</replaceable> ]
[ CYCLE <replaceable>column_name</replaceable> [, ...] SET <replaceable>cycle_mark_col_name</replaceable> [ TO <replaceable>cycle_mark_value</replaceable> DEFAULT <replaceable>cycle_mark_default</replaceable> ] USING <replaceable>cycle_path_col_name</replaceable> ]
TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
</synopsis>
@ -302,8 +302,10 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
been detected. <replaceable>cycle_mark_value</replaceable> and
<replaceable>cycle_mark_default</replaceable> must be constants and they
must be coercible to a common data type, and the data type must have an
inequality operator. (The SQL standard requires that they be character
strings, but PostgreSQL does not require that.) Furthermore, a column
inequality operator. (The SQL standard requires that they be Boolean
constants or character strings, but PostgreSQL does not require that.) By
default, <literal>TRUE</literal> and <literal>FALSE</literal> (of type
<type>boolean</type>) are used. Furthermore, a column
named <replaceable>cycle_path_col_name</replaceable> will be added to the
result column list of the <literal>WITH</literal> query. This column is
used internally for tracking visited rows. See <xref