Adjust cycle detection examples and tests

Adjust the existing cycle detection example and test queries to put
the cycle column before the path column.  This is mainly because the
SQL-standard CYCLE clause puts them in that order, and so if we added
that feature that would make the sequence of examples more consistent
and easier to follow.

Discussion: https://www.postgresql.org/message-id/c5603982-0088-7f14-0caa-fdcd0c837b57@2ndquadrant.com

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>

src/test/regress/expected/with.out

@@ -579,79 +579,79 @@ insert into graph values
 	(1, 4, 'arc 1 -> 4'),
 	(4, 5, 'arc 4 -> 5'),
 	(5, 1, 'arc 5 -> 1');
-with recursive search_graph(f, t, label, path, cycle) as (
-	select *, array[row(g.f, g.t)], false from graph g
+with recursive search_graph(f, t, label, is_cycle, path) as (
+	select *, false, array[row(g.f, g.t)] from graph g
 	union all
-	select g.*, path || row(g.f, g.t), row(g.f, g.t) = any(path)
+	select g.*, row(g.f, g.t) = any(path), path || row(g.f, g.t)
 	from graph g, search_graph sg
-	where g.f = sg.t and not cycle
+	where g.f = sg.t and not is_cycle
 )
 select * from search_graph;
- f | t |   label    |                   path                    | cycle 
----+---+------------+-------------------------------------------+-------
- 1 | 2 | arc 1 -> 2 | {"(1,2)"}                                 | f
- 1 | 3 | arc 1 -> 3 | {"(1,3)"}                                 | f
- 2 | 3 | arc 2 -> 3 | {"(2,3)"}                                 | f
- 1 | 4 | arc 1 -> 4 | {"(1,4)"}                                 | f
- 4 | 5 | arc 4 -> 5 | {"(4,5)"}                                 | f
- 5 | 1 | arc 5 -> 1 | {"(5,1)"}                                 | f
- 1 | 2 | arc 1 -> 2 | {"(5,1)","(1,2)"}                         | f
- 1 | 3 | arc 1 -> 3 | {"(5,1)","(1,3)"}                         | f
- 1 | 4 | arc 1 -> 4 | {"(5,1)","(1,4)"}                         | f
- 2 | 3 | arc 2 -> 3 | {"(1,2)","(2,3)"}                         | f
- 4 | 5 | arc 4 -> 5 | {"(1,4)","(4,5)"}                         | f
- 5 | 1 | arc 5 -> 1 | {"(4,5)","(5,1)"}                         | f
- 1 | 2 | arc 1 -> 2 | {"(4,5)","(5,1)","(1,2)"}                 | f
- 1 | 3 | arc 1 -> 3 | {"(4,5)","(5,1)","(1,3)"}                 | f
- 1 | 4 | arc 1 -> 4 | {"(4,5)","(5,1)","(1,4)"}                 | f
- 2 | 3 | arc 2 -> 3 | {"(5,1)","(1,2)","(2,3)"}                 | f
- 4 | 5 | arc 4 -> 5 | {"(5,1)","(1,4)","(4,5)"}                 | f
- 5 | 1 | arc 5 -> 1 | {"(1,4)","(4,5)","(5,1)"}                 | f
- 1 | 2 | arc 1 -> 2 | {"(1,4)","(4,5)","(5,1)","(1,2)"}         | f
- 1 | 3 | arc 1 -> 3 | {"(1,4)","(4,5)","(5,1)","(1,3)"}         | f
- 1 | 4 | arc 1 -> 4 | {"(1,4)","(4,5)","(5,1)","(1,4)"}         | t
- 2 | 3 | arc 2 -> 3 | {"(4,5)","(5,1)","(1,2)","(2,3)"}         | f
- 4 | 5 | arc 4 -> 5 | {"(4,5)","(5,1)","(1,4)","(4,5)"}         | t
- 5 | 1 | arc 5 -> 1 | {"(5,1)","(1,4)","(4,5)","(5,1)"}         | t
- 2 | 3 | arc 2 -> 3 | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"} | f
+ f | t |   label    | is_cycle |                   path                    
+---+---+------------+----------+-------------------------------------------
+ 1 | 2 | arc 1 -> 2 | f        | {"(1,2)"}
+ 1 | 3 | arc 1 -> 3 | f        | {"(1,3)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(2,3)"}
+ 1 | 4 | arc 1 -> 4 | f        | {"(1,4)"}
+ 4 | 5 | arc 4 -> 5 | f        | {"(4,5)"}
+ 5 | 1 | arc 5 -> 1 | f        | {"(5,1)"}
+ 1 | 2 | arc 1 -> 2 | f        | {"(5,1)","(1,2)"}
+ 1 | 3 | arc 1 -> 3 | f        | {"(5,1)","(1,3)"}
+ 1 | 4 | arc 1 -> 4 | f        | {"(5,1)","(1,4)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(1,2)","(2,3)"}
+ 4 | 5 | arc 4 -> 5 | f        | {"(1,4)","(4,5)"}
+ 5 | 1 | arc 5 -> 1 | f        | {"(4,5)","(5,1)"}
+ 1 | 2 | arc 1 -> 2 | f        | {"(4,5)","(5,1)","(1,2)"}
+ 1 | 3 | arc 1 -> 3 | f        | {"(4,5)","(5,1)","(1,3)"}
+ 1 | 4 | arc 1 -> 4 | f        | {"(4,5)","(5,1)","(1,4)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(5,1)","(1,2)","(2,3)"}
+ 4 | 5 | arc 4 -> 5 | f        | {"(5,1)","(1,4)","(4,5)"}
+ 5 | 1 | arc 5 -> 1 | f        | {"(1,4)","(4,5)","(5,1)"}
+ 1 | 2 | arc 1 -> 2 | f        | {"(1,4)","(4,5)","(5,1)","(1,2)"}
+ 1 | 3 | arc 1 -> 3 | f        | {"(1,4)","(4,5)","(5,1)","(1,3)"}
+ 1 | 4 | arc 1 -> 4 | t        | {"(1,4)","(4,5)","(5,1)","(1,4)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(4,5)","(5,1)","(1,2)","(2,3)"}
+ 4 | 5 | arc 4 -> 5 | t        | {"(4,5)","(5,1)","(1,4)","(4,5)"}
+ 5 | 1 | arc 5 -> 1 | t        | {"(5,1)","(1,4)","(4,5)","(5,1)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"}
 (25 rows)
 
 -- ordering by the path column has same effect as SEARCH DEPTH FIRST
-with recursive search_graph(f, t, label, path, cycle) as (
-	select *, array[row(g.f, g.t)], false from graph g
+with recursive search_graph(f, t, label, is_cycle, path) as (
+	select *, false, array[row(g.f, g.t)] from graph g
 	union all
-	select g.*, path || row(g.f, g.t), row(g.f, g.t) = any(path)
+	select g.*, row(g.f, g.t) = any(path), path || row(g.f, g.t)
 	from graph g, search_graph sg
-	where g.f = sg.t and not cycle
+	where g.f = sg.t and not is_cycle
 )
 select * from search_graph order by path;
- f | t |   label    |                   path                    | cycle 
----+---+------------+-------------------------------------------+-------
- 1 | 2 | arc 1 -> 2 | {"(1,2)"}                                 | f
- 2 | 3 | arc 2 -> 3 | {"(1,2)","(2,3)"}                         | f
- 1 | 3 | arc 1 -> 3 | {"(1,3)"}                                 | f
- 1 | 4 | arc 1 -> 4 | {"(1,4)"}                                 | f
- 4 | 5 | arc 4 -> 5 | {"(1,4)","(4,5)"}                         | f
- 5 | 1 | arc 5 -> 1 | {"(1,4)","(4,5)","(5,1)"}                 | f
- 1 | 2 | arc 1 -> 2 | {"(1,4)","(4,5)","(5,1)","(1,2)"}         | f
- 2 | 3 | arc 2 -> 3 | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"} | f
- 1 | 3 | arc 1 -> 3 | {"(1,4)","(4,5)","(5,1)","(1,3)"}         | f
- 1 | 4 | arc 1 -> 4 | {"(1,4)","(4,5)","(5,1)","(1,4)"}         | t
- 2 | 3 | arc 2 -> 3 | {"(2,3)"}                                 | f
- 4 | 5 | arc 4 -> 5 | {"(4,5)"}                                 | f
- 5 | 1 | arc 5 -> 1 | {"(4,5)","(5,1)"}                         | f
- 1 | 2 | arc 1 -> 2 | {"(4,5)","(5,1)","(1,2)"}                 | f
- 2 | 3 | arc 2 -> 3 | {"(4,5)","(5,1)","(1,2)","(2,3)"}         | f
- 1 | 3 | arc 1 -> 3 | {"(4,5)","(5,1)","(1,3)"}                 | f
- 1 | 4 | arc 1 -> 4 | {"(4,5)","(5,1)","(1,4)"}                 | f
- 4 | 5 | arc 4 -> 5 | {"(4,5)","(5,1)","(1,4)","(4,5)"}         | t
- 5 | 1 | arc 5 -> 1 | {"(5,1)"}                                 | f
- 1 | 2 | arc 1 -> 2 | {"(5,1)","(1,2)"}                         | f
- 2 | 3 | arc 2 -> 3 | {"(5,1)","(1,2)","(2,3)"}                 | f
- 1 | 3 | arc 1 -> 3 | {"(5,1)","(1,3)"}                         | f
- 1 | 4 | arc 1 -> 4 | {"(5,1)","(1,4)"}                         | f
- 4 | 5 | arc 4 -> 5 | {"(5,1)","(1,4)","(4,5)"}                 | f
- 5 | 1 | arc 5 -> 1 | {"(5,1)","(1,4)","(4,5)","(5,1)"}         | t
+ f | t |   label    | is_cycle |                   path                    
+---+---+------------+----------+-------------------------------------------
+ 1 | 2 | arc 1 -> 2 | f        | {"(1,2)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(1,2)","(2,3)"}
+ 1 | 3 | arc 1 -> 3 | f        | {"(1,3)"}
+ 1 | 4 | arc 1 -> 4 | f        | {"(1,4)"}
+ 4 | 5 | arc 4 -> 5 | f        | {"(1,4)","(4,5)"}
+ 5 | 1 | arc 5 -> 1 | f        | {"(1,4)","(4,5)","(5,1)"}
+ 1 | 2 | arc 1 -> 2 | f        | {"(1,4)","(4,5)","(5,1)","(1,2)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"}
+ 1 | 3 | arc 1 -> 3 | f        | {"(1,4)","(4,5)","(5,1)","(1,3)"}
+ 1 | 4 | arc 1 -> 4 | t        | {"(1,4)","(4,5)","(5,1)","(1,4)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(2,3)"}
+ 4 | 5 | arc 4 -> 5 | f        | {"(4,5)"}
+ 5 | 1 | arc 5 -> 1 | f        | {"(4,5)","(5,1)"}
+ 1 | 2 | arc 1 -> 2 | f        | {"(4,5)","(5,1)","(1,2)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(4,5)","(5,1)","(1,2)","(2,3)"}
+ 1 | 3 | arc 1 -> 3 | f        | {"(4,5)","(5,1)","(1,3)"}
+ 1 | 4 | arc 1 -> 4 | f        | {"(4,5)","(5,1)","(1,4)"}
+ 4 | 5 | arc 4 -> 5 | t        | {"(4,5)","(5,1)","(1,4)","(4,5)"}
+ 5 | 1 | arc 5 -> 1 | f        | {"(5,1)"}
+ 1 | 2 | arc 1 -> 2 | f        | {"(5,1)","(1,2)"}
+ 2 | 3 | arc 2 -> 3 | f        | {"(5,1)","(1,2)","(2,3)"}
+ 1 | 3 | arc 1 -> 3 | f        | {"(5,1)","(1,3)"}
+ 1 | 4 | arc 1 -> 4 | f        | {"(5,1)","(1,4)"}
+ 4 | 5 | arc 4 -> 5 | f        | {"(5,1)","(1,4)","(4,5)"}
+ 5 | 1 | arc 5 -> 1 | t        | {"(5,1)","(1,4)","(4,5)","(5,1)"}
 (25 rows)
 
 --

src/test/regress/sql/with.sql

@@ -308,22 +308,22 @@ insert into graph values
 	(4, 5, 'arc 4 -> 5'),
 	(5, 1, 'arc 5 -> 1');
 
-with recursive search_graph(f, t, label, path, cycle) as (
-	select *, array[row(g.f, g.t)], false from graph g
+with recursive search_graph(f, t, label, is_cycle, path) as (
+	select *, false, array[row(g.f, g.t)] from graph g
 	union all
-	select g.*, path || row(g.f, g.t), row(g.f, g.t) = any(path)
+	select g.*, row(g.f, g.t) = any(path), path || row(g.f, g.t)
 	from graph g, search_graph sg
-	where g.f = sg.t and not cycle
+	where g.f = sg.t and not is_cycle
 )
 select * from search_graph;
 
 -- ordering by the path column has same effect as SEARCH DEPTH FIRST
-with recursive search_graph(f, t, label, path, cycle) as (
-	select *, array[row(g.f, g.t)], false from graph g
+with recursive search_graph(f, t, label, is_cycle, path) as (
+	select *, false, array[row(g.f, g.t)] from graph g
 	union all
-	select g.*, path || row(g.f, g.t), row(g.f, g.t) = any(path)
+	select g.*, row(g.f, g.t) = any(path), path || row(g.f, g.t)
 	from graph g, search_graph sg
-	where g.f = sg.t and not cycle
+	where g.f = sg.t and not is_cycle
 )
 select * from search_graph order by path;