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Fix EXPLAIN of SEARCH BREADTH FIRST with a constant initial value.

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If the non-recursive term of a SEARCH BREADTH FIRST recursive
query has only constants in its target list, the planner will
fold the starting RowExpr added by rewrite into a simple Const
of type RECORD.  The executor doesn't have any problem with
that --- but EXPLAIN VERBOSE will encounter the Const as the
ultimate source of truth about what the field names of the
SET column are, and it didn't know what to do with that.
Fortunately, we can pull the identifying typmod out of the
Const, in much the same way that record_out would.

For reasons that remain a bit obscure to me, this only fails
with SEARCH BREADTH FIRST, not SEARCH DEPTH FIRST or CYCLE.
But I added regression test cases for both of those options
too, just to make sure we don't break it in future.

Per bug #17644 from Matthijs van der Vleuten.  Back-patch
to v14 where these constructs were added.

Discussion: https://postgr.es/m/17644-3bd1f3036d6d7a16@postgresql.org
This commit is contained in:
Tom Lane
2022-10-16 19:18:08 -04:00
parent 18e60712dd
commit 8122160ffb
4 changed files with 208 additions and 1 deletions
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120
src/test/regress/expected/with.out
View File

@@ -790,6 +790,83 @@ select * from search_graph order by seq;
4 | 5 | arc 4 -> 5 | (1,4,5)
(7 rows)
-- a constant initial value causes issues for EXPLAIN
explain (verbose, costs off)
with recursive test as (
select 1 as x
union all
select x + 1
from test
) search depth first by x set y
select * from test limit 5;
QUERY PLAN
-----------------------------------------------------------------------------------------
Limit
Output: test.x, test.y
CTE test
-> Recursive Union
-> Result
Output: 1, '{(1)}'::record[]
-> WorkTable Scan on test test_1
Output: (test_1.x + 1), array_cat(test_1.y, ARRAY[ROW((test_1.x + 1))])
-> CTE Scan on test
Output: test.x, test.y
(10 rows)
with recursive test as (
select 1 as x
union all
select x + 1
from test
) search depth first by x set y
select * from test limit 5;
x | y
---+-----------------------
1 | {(1)}
2 | {(1),(2)}
3 | {(1),(2),(3)}
4 | {(1),(2),(3),(4)}
5 | {(1),(2),(3),(4),(5)}
(5 rows)
explain (verbose, costs off)
with recursive test as (
select 1 as x
union all
select x + 1
from test
) search breadth first by x set y
select * from test limit 5;
QUERY PLAN
--------------------------------------------------------------------------------------------
Limit
Output: test.x, test.y
CTE test
-> Recursive Union
-> Result
Output: 1, '(0,1)'::record
-> WorkTable Scan on test test_1
Output: (test_1.x + 1), ROW(int8inc((test_1.y)."*DEPTH*"), (test_1.x + 1))
-> CTE Scan on test
Output: test.x, test.y
(10 rows)
with recursive test as (
select 1 as x
union all
select x + 1
from test
) search breadth first by x set y
select * from test limit 5;
x | y
---+-------
1 | (0,1)
2 | (1,2)
3 | (2,3)
4 | (3,4)
5 | (4,5)
(5 rows)
-- various syntax errors
with recursive search_graph(f, t, label) as (
select * from graph0 g
@@ -1101,6 +1178,49 @@ select * from search_graph;
2 | 3 | arc 2 -> 3 | N | {"(1,4)","(4,5)","(5,1)","(1,2)","(2,3)"}
(25 rows)
explain (verbose, costs off)
with recursive test as (
select 0 as x
union all
select (x + 1) % 10
from test
) cycle x set is_cycle using path
select * from test;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
CTE Scan on test
Output: test.x, test.is_cycle, test.path
CTE test
-> Recursive Union
-> Result
Output: 0, false, '{(0)}'::record[]
-> WorkTable Scan on test test_1
Output: ((test_1.x + 1) % 10), CASE WHEN (ROW(((test_1.x + 1) % 10)) = ANY (test_1.path)) THEN true ELSE false END, array_cat(test_1.path, ARRAY[ROW(((test_1.x + 1) % 10))])
Filter: (NOT test_1.is_cycle)
(9 rows)
with recursive test as (
select 0 as x
union all
select (x + 1) % 10
from test
) cycle x set is_cycle using path
select * from test;
x | is_cycle | path
---+----------+-----------------------------------------------
0 | f | {(0)}
1 | f | {(0),(1)}
2 | f | {(0),(1),(2)}
3 | f | {(0),(1),(2),(3)}
4 | f | {(0),(1),(2),(3),(4)}
5 | f | {(0),(1),(2),(3),(4),(5)}
6 | f | {(0),(1),(2),(3),(4),(5),(6)}
7 | f | {(0),(1),(2),(3),(4),(5),(6),(7)}
8 | f | {(0),(1),(2),(3),(4),(5),(6),(7),(8)}
9 | f | {(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)}
0 | t | {(0),(1),(2),(3),(4),(5),(6),(7),(8),(9),(0)}
(11 rows)
-- multiple CTEs
with recursive
graph(f, t, label) as (

52
src/test/regress/sql/with.sql
View File

@@ -414,6 +414,41 @@ with recursive search_graph(f, t, label) as (
) search breadth first by f, t set seq
select * from search_graph order by seq;
-- a constant initial value causes issues for EXPLAIN
explain (verbose, costs off)
with recursive test as (
select 1 as x
union all
select x + 1
from test
) search depth first by x set y
select * from test limit 5;
with recursive test as (
select 1 as x
union all
select x + 1
from test
) search depth first by x set y
select * from test limit 5;
explain (verbose, costs off)
with recursive test as (
select 1 as x
union all
select x + 1
from test
) search breadth first by x set y
select * from test limit 5;
with recursive test as (
select 1 as x
union all
select x + 1
from test
) search breadth first by x set y
select * from test limit 5;
-- various syntax errors
with recursive search_graph(f, t, label) as (
select * from graph0 g
@@ -553,6 +588,23 @@ with recursive search_graph(f, t, label) as (
) cycle f, t set is_cycle to 'Y' default 'N' using path
select * from search_graph;
explain (verbose, costs off)
with recursive test as (
select 0 as x
union all
select (x + 1) % 10
from test
) cycle x set is_cycle using path
select * from test;
with recursive test as (
select 0 as x
union all
select (x + 1) % 10
from test
) cycle x set is_cycle using path
select * from test;
-- multiple CTEs
with recursive
graph(f, t, label) as (