diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/queries.sgml | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/doc/src/sgml/queries.sgml b/doc/src/sgml/queries.sgml index 77fb1991aeb..bad97a75b27 100644 --- a/doc/src/sgml/queries.sgml +++ b/doc/src/sgml/queries.sgml @@ -2144,20 +2144,20 @@ SELECT * FROM search_graph; <literal>UNION ALL</literal> to <literal>UNION</literal> would not eliminate the looping. Instead we need to recognize whether we have reached the same row again while following a particular path of links. We add two columns - <structfield>path</structfield> and <structfield>cycle</structfield> to the loop-prone query: + <structfield>is_cycle</structfield> and <structfield>path</structfield> to the loop-prone query: <programlisting> -WITH RECURSIVE search_graph(id, link, data, depth, path, cycle) AS ( +WITH RECURSIVE search_graph(id, link, data, depth, is_cycle, path) AS ( SELECT g.id, g.link, g.data, 1, - ARRAY[g.id], - false + false, + ARRAY[g.id] FROM graph g UNION ALL SELECT g.id, g.link, g.data, sg.depth + 1, - path || g.id, - g.id = ANY(path) + g.id = ANY(path), + path || g.id FROM graph g, search_graph sg - WHERE g.id = sg.link AND NOT cycle + WHERE g.id = sg.link AND NOT is_cycle ) SELECT * FROM search_graph; </programlisting> @@ -2172,17 +2172,17 @@ SELECT * FROM search_graph; compare fields <structfield>f1</structfield> and <structfield>f2</structfield>: <programlisting> -WITH RECURSIVE search_graph(id, link, data, depth, path, cycle) AS ( +WITH RECURSIVE search_graph(id, link, data, depth, is_cycle, path) AS ( SELECT g.id, g.link, g.data, 1, - ARRAY[ROW(g.f1, g.f2)], - false + false, + ARRAY[ROW(g.f1, g.f2)] FROM graph g UNION ALL SELECT g.id, g.link, g.data, sg.depth + 1, - path || ROW(g.f1, g.f2), - ROW(g.f1, g.f2) = ANY(path) + ROW(g.f1, g.f2) = ANY(path), + path || ROW(g.f1, g.f2) FROM graph g, search_graph sg - WHERE g.id = sg.link AND NOT cycle + WHERE g.id = sg.link AND NOT is_cycle ) SELECT * FROM search_graph; </programlisting> |