Fix planner failure with full join in RHS of left join.

Given a left join containing a full join in its righthand side, with
the left join's joinclause referencing only one side of the full join
(in a non-strict fashion, so that the full join doesn't get simplified),
the planner could fail with "failed to build any N-way joins" or related
errors.  This happened because the full join was seen as overlapping the
left join's RHS, and then recent changes within join_is_legal() caused
that function to conclude that the full join couldn't validly be formed.
Rather than try to rejigger join_is_legal() yet more to allow this,
I think it's better to fix initsplan.c so that the required join order
is explicit in the SpecialJoinInfo data structure.  The previous coding
there essentially ignored full joins, relying on the fact that we don't
flatten them in the joinlist data structure to preserve their ordering.
That's sufficient to prevent a wrong plan from being formed, but as this
example shows, it's not sufficient to ensure that the right plan will
be formed.  We need to work a bit harder to ensure that the right plan
looks sane according to the SpecialJoinInfos.

Per bug #14105 from Vojtech Rylko.  This was apparently induced by
commit 8703059c6 (though now that I've seen it, I wonder whether there
are related cases that could have failed before that); so back-patch
to all active branches.  Unfortunately, that patch also went into 9.0,
so this bug is a regression that won't be fixed in that branch.

diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 6dc01812daf8d43b5f4b0c8d56c8031efd61028f..cd132ccfce7067ab87ed2786adffd3586c3e09c2 100644 (file)
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -648,9 +648,32 @@ make_outerjoininfo(PlannerInfo *root,
        {
                SpecialJoinInfo *otherinfo = (SpecialJoinInfo *) lfirst(l);
 
-               /* ignore full joins --- other mechanisms preserve their ordering */
+               /*
+                * A full join is an optimization barrier: we can't associate into or
+                * out of it.  Hence, if it overlaps either LHS or RHS of the current
+                * rel, expand that side's min relset to cover the whole full join.
+                */
                if (otherinfo->jointype == JOIN_FULL)
+               {
+                       if (bms_overlap(left_rels, otherinfo->syn_lefthand) ||
+                               bms_overlap(left_rels, otherinfo->syn_righthand))
+                       {
+                               min_lefthand = bms_add_members(min_lefthand,
+                                                                                          otherinfo->syn_lefthand);
+                               min_lefthand = bms_add_members(min_lefthand,
+                                                                                          otherinfo->syn_righthand);
+                       }
+                       if (bms_overlap(right_rels, otherinfo->syn_lefthand) ||
+                               bms_overlap(right_rels, otherinfo->syn_righthand))
+                       {
+                               min_righthand = bms_add_members(min_righthand,
+                                                                                               otherinfo->syn_lefthand);
+                               min_righthand = bms_add_members(min_righthand,
+                                                                                               otherinfo->syn_righthand);
+                       }
+                       /* Needn't do anything else with the full join */
                        continue;
+               }
 
                /*
                 * For a lower OJ in our LHS, if our join condition uses the lower

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index e69d5cccbc04baa6bbb758cc65395cc16f699e79..d3c20d2e959db34a7813c4842094e970b1e9f06d 100644 (file)
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3048,6 +3048,37 @@ select * from
  doh! | 123 | 456 | hi de ho neighbor |   
 (2 rows)
 
+--
+-- test successful handling of full join underneath left join (bug #14105)
+--
+explain (costs off)
+select * from
+  (select 1 as id) as xx
+  left join
+    (tenk1 as a1 full join (select 1 as id) as yy on (a1.unique1 = yy.id))
+  on (xx.id = coalesce(yy.id));
+              QUERY PLAN               
+---------------------------------------
+ Nested Loop Left Join
+   Join Filter: ((1) = COALESCE((1)))
+   ->  Result
+   ->  Hash Full Join
+         Hash Cond: (a1.unique1 = (1))
+         ->  Seq Scan on tenk1 a1
+         ->  Hash
+               ->  Result
+(8 rows)
+
+select * from
+  (select 1 as id) as xx
+  left join
+    (tenk1 as a1 full join (select 1 as id) as yy on (a1.unique1 = yy.id))
+  on (xx.id = coalesce(yy.id));
+ id | unique1 | unique2 | two | four | ten | twenty | hundred | thousand | twothousand | fivethous | tenthous | odd | even | stringu1 | stringu2 | string4 | id 
+----+---------+---------+-----+------+-----+--------+---------+----------+-------------+-----------+----------+-----+------+----------+----------+---------+----
+  1 |       1 |    2838 |   1 |    1 |   1 |      1 |       1 |        1 |           1 |         1 |        1 |   2 |    3 | BAAAAA   | EFEAAA   | OOOOxx  |  1
+(1 row)
+
 --
 -- test ability to push constants through outer join clauses
 --

diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index fdeca0ba71908fda1146ad782a95b32a95b43fb2..8ec74d9b4a32e9b125edffd47cc3cf3a21d44c6f 100644 (file)
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -851,6 +851,23 @@ select * from
   left join int4_tbl i4
   on i8.q1 = i4.f1;
 
+--
+-- test successful handling of full join underneath left join (bug #14105)
+--
+
+explain (costs off)
+select * from
+  (select 1 as id) as xx
+  left join
+    (tenk1 as a1 full join (select 1 as id) as yy on (a1.unique1 = yy.id))
+  on (xx.id = coalesce(yy.id));
+
+select * from
+  (select 1 as id) as xx
+  left join
+    (tenk1 as a1 full join (select 1 as id) as yy on (a1.unique1 = yy.id))
+  on (xx.id = coalesce(yy.id));
+
 --
 -- test ability to push constants through outer join clauses
 --