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
This commit is contained in:
Peter Eisentraut
parent
88ea7a1188
commit
3fb676504d
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@ -2144,20 +2144,20 @@ SELECT * FROM search_graph;
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<literal>UNION ALL</literal> to <literal>UNION</literal> would not eliminate the looping.
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Instead we need to recognize whether we have reached the same row again
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while following a particular path of links. We add two columns
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<structfield>path</structfield> and <structfield>cycle</structfield> to the loop-prone query:
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<structfield>is_cycle</structfield> and <structfield>path</structfield> to the loop-prone query:
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<programlisting>
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WITH RECURSIVE search_graph(id, link, data, depth, path, cycle) AS (
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WITH RECURSIVE search_graph(id, link, data, depth, is_cycle, path) AS (
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SELECT g.id, g.link, g.data, 1,
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ARRAY[g.id],
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false
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false,
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ARRAY[g.id]
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FROM graph g
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UNION ALL
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SELECT g.id, g.link, g.data, sg.depth + 1,
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path || g.id,
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g.id = ANY(path)
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g.id = ANY(path),
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path || g.id
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FROM graph g, search_graph sg
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WHERE g.id = sg.link AND NOT cycle
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WHERE g.id = sg.link AND NOT is_cycle
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)
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SELECT * FROM search_graph;
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</programlisting>
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@ -2172,17 +2172,17 @@ SELECT * FROM search_graph;
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compare fields <structfield>f1</structfield> and <structfield>f2</structfield>:
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<programlisting>
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WITH RECURSIVE search_graph(id, link, data, depth, path, cycle) AS (
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WITH RECURSIVE search_graph(id, link, data, depth, is_cycle, path) AS (
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SELECT g.id, g.link, g.data, 1,
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ARRAY[ROW(g.f1, g.f2)],
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false
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false,
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ARRAY[ROW(g.f1, g.f2)]
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FROM graph g
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UNION ALL
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SELECT g.id, g.link, g.data, sg.depth + 1,
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path || ROW(g.f1, g.f2),
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ROW(g.f1, g.f2) = ANY(path)
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ROW(g.f1, g.f2) = ANY(path),
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path || ROW(g.f1, g.f2)
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FROM graph g, search_graph sg
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WHERE g.id = sg.link AND NOT cycle
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WHERE g.id = sg.link AND NOT is_cycle
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)
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SELECT * FROM search_graph;
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</programlisting>
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@ -579,79 +579,79 @@ insert into graph values
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(1, 4, 'arc 1 -> 4'),
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(4, 5, 'arc 4 -> 5'),
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(5, 1, 'arc 5 -> 1');
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with recursive search_graph(f, t, label, path, cycle) as (
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select *, array[row(g.f, g.t)], false from graph g
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with recursive search_graph(f, t, label, is_cycle, path) as (
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select *, false, array[row(g.f, g.t)] from graph g
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union all
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select g.*, path || row(g.f, g.t), row(g.f, g.t) = any(path)
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select g.*, row(g.f, g.t) = any(path), path || row(g.f, g.t)
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from graph g, search_graph sg
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where g.f = sg.t and not cycle
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where g.f = sg.t and not is_cycle
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)
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select * from search_graph;
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f | t | label | path | cycle
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---+---+------------+-------------------------------------------+-------
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1 | 2 | arc 1 -> 2 | {"(1,2)"} | f
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1 | 3 | arc 1 -> 3 | {"(1,3)"} | f
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2 | 3 | arc 2 -> 3 | {"(2,3)"} | f
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1 | 4 | arc 1 -> 4 | {"(1,4)"} | f
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4 | 5 | arc 4 -> 5 | {"(4,5)"} | f
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5 | 1 | arc 5 -> 1 | {"(5,1)"} | f
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1 | 2 | arc 1 -> 2 | {"(5,1)","(1,2)"} | f
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1 | 3 | arc 1 -> 3 | {"(5,1)","(1,3)"} | f
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1 | 4 | arc 1 -> 4 | {"(5,1)","(1,4)"} | f
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2 | 3 | arc 2 -> 3 | {"(1,2)","(2,3)"} | f
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4 | 5 | arc 4 -> 5 | {"(1,4)","(4,5)"} | f
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5 | 1 | arc 5 -> 1 | {"(4,5)","(5,1)"} | f
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1 | 2 | arc 1 -> 2 | {"(4,5)","(5,1)","(1,2)"} | f
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1 | 3 | arc 1 -> 3 | {"(4,5)","(5,1)","(1,3)"} | f
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1 | 4 | arc 1 -> 4 | {"(4,5)","(5,1)","(1,4)"} | f
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2 | 3 | arc 2 -> 3 | {"(5,1)","(1,2)","(2,3)"} | f
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4 | 5 | arc 4 -> 5 | {"(5,1)","(1,4)","(4,5)"} | f
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5 | 1 | arc 5 -> 1 | {"(1,4)","(4,5)","(5,1)"} | f
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1 | 2 | arc 1 -> 2 | {"(1,4)","(4,5)","(5,1)","(1,2)"} | f
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1 | 3 | arc 1 -> 3 | {"(1,4)","(4,5)","(5,1)","(1,3)"} | f
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1 | 4 | arc 1 -> 4 | {"(1,4)","(4,5)","(5,1)","(1,4)"} | t
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2 | 3 | arc 2 -> 3 | {"(4,5)","(5,1)","(1,2)","(2,3)"} | f
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4 | 5 | arc 4 -> 5 | {"(4,5)","(5,1)","(1,4)","(4,5)"} | t
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5 | 1 | arc 5 -> 1 | {"(5,1)","(1,4)","(4,5)","(5,1)"} | t
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2 | 3 | arc 2 -> 3 | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"} | f
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f | t | label | is_cycle | path
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---+---+------------+----------+-------------------------------------------
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1 | 2 | arc 1 -> 2 | f | {"(1,2)"}
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1 | 3 | arc 1 -> 3 | f | {"(1,3)"}
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2 | 3 | arc 2 -> 3 | f | {"(2,3)"}
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1 | 4 | arc 1 -> 4 | f | {"(1,4)"}
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4 | 5 | arc 4 -> 5 | f | {"(4,5)"}
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5 | 1 | arc 5 -> 1 | f | {"(5,1)"}
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1 | 2 | arc 1 -> 2 | f | {"(5,1)","(1,2)"}
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1 | 3 | arc 1 -> 3 | f | {"(5,1)","(1,3)"}
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1 | 4 | arc 1 -> 4 | f | {"(5,1)","(1,4)"}
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2 | 3 | arc 2 -> 3 | f | {"(1,2)","(2,3)"}
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4 | 5 | arc 4 -> 5 | f | {"(1,4)","(4,5)"}
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5 | 1 | arc 5 -> 1 | f | {"(4,5)","(5,1)"}
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1 | 2 | arc 1 -> 2 | f | {"(4,5)","(5,1)","(1,2)"}
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1 | 3 | arc 1 -> 3 | f | {"(4,5)","(5,1)","(1,3)"}
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1 | 4 | arc 1 -> 4 | f | {"(4,5)","(5,1)","(1,4)"}
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2 | 3 | arc 2 -> 3 | f | {"(5,1)","(1,2)","(2,3)"}
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4 | 5 | arc 4 -> 5 | f | {"(5,1)","(1,4)","(4,5)"}
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5 | 1 | arc 5 -> 1 | f | {"(1,4)","(4,5)","(5,1)"}
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1 | 2 | arc 1 -> 2 | f | {"(1,4)","(4,5)","(5,1)","(1,2)"}
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1 | 3 | arc 1 -> 3 | f | {"(1,4)","(4,5)","(5,1)","(1,3)"}
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1 | 4 | arc 1 -> 4 | t | {"(1,4)","(4,5)","(5,1)","(1,4)"}
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2 | 3 | arc 2 -> 3 | f | {"(4,5)","(5,1)","(1,2)","(2,3)"}
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4 | 5 | arc 4 -> 5 | t | {"(4,5)","(5,1)","(1,4)","(4,5)"}
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5 | 1 | arc 5 -> 1 | t | {"(5,1)","(1,4)","(4,5)","(5,1)"}
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2 | 3 | arc 2 -> 3 | f | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"}
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(25 rows)
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-- ordering by the path column has same effect as SEARCH DEPTH FIRST
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with recursive search_graph(f, t, label, path, cycle) as (
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select *, array[row(g.f, g.t)], false from graph g
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with recursive search_graph(f, t, label, is_cycle, path) as (
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select *, false, array[row(g.f, g.t)] from graph g
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union all
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select g.*, path || row(g.f, g.t), row(g.f, g.t) = any(path)
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select g.*, row(g.f, g.t) = any(path), path || row(g.f, g.t)
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from graph g, search_graph sg
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where g.f = sg.t and not cycle
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where g.f = sg.t and not is_cycle
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)
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select * from search_graph order by path;
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f | t | label | path | cycle
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---+---+------------+-------------------------------------------+-------
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1 | 2 | arc 1 -> 2 | {"(1,2)"} | f
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2 | 3 | arc 2 -> 3 | {"(1,2)","(2,3)"} | f
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1 | 3 | arc 1 -> 3 | {"(1,3)"} | f
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1 | 4 | arc 1 -> 4 | {"(1,4)"} | f
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4 | 5 | arc 4 -> 5 | {"(1,4)","(4,5)"} | f
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5 | 1 | arc 5 -> 1 | {"(1,4)","(4,5)","(5,1)"} | f
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1 | 2 | arc 1 -> 2 | {"(1,4)","(4,5)","(5,1)","(1,2)"} | f
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2 | 3 | arc 2 -> 3 | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"} | f
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1 | 3 | arc 1 -> 3 | {"(1,4)","(4,5)","(5,1)","(1,3)"} | f
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1 | 4 | arc 1 -> 4 | {"(1,4)","(4,5)","(5,1)","(1,4)"} | t
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2 | 3 | arc 2 -> 3 | {"(2,3)"} | f
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4 | 5 | arc 4 -> 5 | {"(4,5)"} | f
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5 | 1 | arc 5 -> 1 | {"(4,5)","(5,1)"} | f
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1 | 2 | arc 1 -> 2 | {"(4,5)","(5,1)","(1,2)"} | f
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2 | 3 | arc 2 -> 3 | {"(4,5)","(5,1)","(1,2)","(2,3)"} | f
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1 | 3 | arc 1 -> 3 | {"(4,5)","(5,1)","(1,3)"} | f
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1 | 4 | arc 1 -> 4 | {"(4,5)","(5,1)","(1,4)"} | f
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4 | 5 | arc 4 -> 5 | {"(4,5)","(5,1)","(1,4)","(4,5)"} | t
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5 | 1 | arc 5 -> 1 | {"(5,1)"} | f
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1 | 2 | arc 1 -> 2 | {"(5,1)","(1,2)"} | f
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2 | 3 | arc 2 -> 3 | {"(5,1)","(1,2)","(2,3)"} | f
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1 | 3 | arc 1 -> 3 | {"(5,1)","(1,3)"} | f
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1 | 4 | arc 1 -> 4 | {"(5,1)","(1,4)"} | f
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4 | 5 | arc 4 -> 5 | {"(5,1)","(1,4)","(4,5)"} | f
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5 | 1 | arc 5 -> 1 | {"(5,1)","(1,4)","(4,5)","(5,1)"} | t
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f | t | label | is_cycle | path
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---+---+------------+----------+-------------------------------------------
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1 | 2 | arc 1 -> 2 | f | {"(1,2)"}
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2 | 3 | arc 2 -> 3 | f | {"(1,2)","(2,3)"}
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1 | 3 | arc 1 -> 3 | f | {"(1,3)"}
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1 | 4 | arc 1 -> 4 | f | {"(1,4)"}
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4 | 5 | arc 4 -> 5 | f | {"(1,4)","(4,5)"}
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5 | 1 | arc 5 -> 1 | f | {"(1,4)","(4,5)","(5,1)"}
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1 | 2 | arc 1 -> 2 | f | {"(1,4)","(4,5)","(5,1)","(1,2)"}
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2 | 3 | arc 2 -> 3 | f | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"}
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1 | 3 | arc 1 -> 3 | f | {"(1,4)","(4,5)","(5,1)","(1,3)"}
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1 | 4 | arc 1 -> 4 | t | {"(1,4)","(4,5)","(5,1)","(1,4)"}
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2 | 3 | arc 2 -> 3 | f | {"(2,3)"}
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4 | 5 | arc 4 -> 5 | f | {"(4,5)"}
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5 | 1 | arc 5 -> 1 | f | {"(4,5)","(5,1)"}
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1 | 2 | arc 1 -> 2 | f | {"(4,5)","(5,1)","(1,2)"}
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2 | 3 | arc 2 -> 3 | f | {"(4,5)","(5,1)","(1,2)","(2,3)"}
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1 | 3 | arc 1 -> 3 | f | {"(4,5)","(5,1)","(1,3)"}
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1 | 4 | arc 1 -> 4 | f | {"(4,5)","(5,1)","(1,4)"}
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4 | 5 | arc 4 -> 5 | t | {"(4,5)","(5,1)","(1,4)","(4,5)"}
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5 | 1 | arc 5 -> 1 | f | {"(5,1)"}
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1 | 2 | arc 1 -> 2 | f | {"(5,1)","(1,2)"}
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2 | 3 | arc 2 -> 3 | f | {"(5,1)","(1,2)","(2,3)"}
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1 | 3 | arc 1 -> 3 | f | {"(5,1)","(1,3)"}
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1 | 4 | arc 1 -> 4 | f | {"(5,1)","(1,4)"}
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4 | 5 | arc 4 -> 5 | f | {"(5,1)","(1,4)","(4,5)"}
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5 | 1 | arc 5 -> 1 | t | {"(5,1)","(1,4)","(4,5)","(5,1)"}
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(25 rows)
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--
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@ -308,22 +308,22 @@ insert into graph values
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(4, 5, 'arc 4 -> 5'),
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(5, 1, 'arc 5 -> 1');
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with recursive search_graph(f, t, label, path, cycle) as (
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select *, array[row(g.f, g.t)], false from graph g
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with recursive search_graph(f, t, label, is_cycle, path) as (
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select *, false, array[row(g.f, g.t)] from graph g
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union all
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select g.*, path || row(g.f, g.t), row(g.f, g.t) = any(path)
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select g.*, row(g.f, g.t) = any(path), path || row(g.f, g.t)
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from graph g, search_graph sg
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where g.f = sg.t and not cycle
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where g.f = sg.t and not is_cycle
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)
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select * from search_graph;
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-- ordering by the path column has same effect as SEARCH DEPTH FIRST
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with recursive search_graph(f, t, label, path, cycle) as (
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select *, array[row(g.f, g.t)], false from graph g
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with recursive search_graph(f, t, label, is_cycle, path) as (
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select *, false, array[row(g.f, g.t)] from graph g
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union all
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select g.*, path || row(g.f, g.t), row(g.f, g.t) = any(path)
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select g.*, row(g.f, g.t) = any(path), path || row(g.f, g.t)
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from graph g, search_graph sg
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where g.f = sg.t and not cycle
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where g.f = sg.t and not is_cycle
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)
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select * from search_graph order by path;
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