Fix another oversight in checking if a join with LATERAL refs is legal.

It was possible for the planner to decide to join a LATERAL subquery to
the outer side of an outer join before the outer join itself is completed.
Normally that's fine because of the associativity rules, but it doesn't
work if the subquery contains a lateral reference to the inner side of the
outer join.  In such a situation the outer join *must* be done first.
join_is_legal() missed this consideration and would allow the join to be
attempted, but the actual path-building code correctly decided that no
valid join path could be made, sometimes leading to planner errors such as
"failed to build any N-way joins".

Per report from Andreas Seltenreich.  Back-patch to 9.3 where LATERAL
support was added.

diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 3c99c8ce49df29e7cd0a6fb36c3f3c41ec27e93d..c0cce0e4bb4c3a38802e8145f65094faf7d43d40 100644 (file)
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -334,6 +334,7 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
        bool            must_be_leftjoin;
        bool            lateral_fwd;
        bool            lateral_rev;
+       Relids          join_lateral_rels;
        ListCell   *l;
 
        /*
@@ -569,6 +570,35 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
                }
        }
 
+       /*
+        * LATERAL references could also cause problems later on if we accept this
+        * join: if the join's minimum parameterization includes any rels that
+        * would have to be on the inside of an outer join with this join rel,
+        * then it's never going to be possible to build the complete query using
+        * this join.  We should reject this join not only because it'll save
+        * work, but because if we don't, the clauseless-join heuristics might
+        * think that legality of this join means that some other join rel need
+        * not be formed, and that could lead to failure to find any plan at all.
+        * It seems best not to merge this check into the main loop above, because
+        * it is concerned with SJs that are not otherwise relevant to this join.
+        */
+       join_lateral_rels = min_join_parameterization(root, joinrelids);
+       if (join_lateral_rels)
+       {
+               foreach(l, root->join_info_list)
+               {
+                       SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
+
+                       if (bms_overlap(sjinfo->min_righthand, join_lateral_rels) &&
+                               bms_overlap(sjinfo->min_lefthand, joinrelids))
+                               return false;   /* will not be able to join to min_righthand */
+                       if (sjinfo->jointype == JOIN_FULL &&
+                               bms_overlap(sjinfo->min_lefthand, join_lateral_rels) &&
+                               bms_overlap(sjinfo->min_righthand, joinrelids))
+                               return false;   /* will not be able to join to min_lefthand */
+               }
+       }
+
        /* Otherwise, it's a valid join */
        *sjinfo_p = match_sjinfo;
        *reversed_p = reversed;

diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 42e0a6eba71cf1b54eb0844fe2631825e4418a3c..fab5cd4d8b9df3fb762039fa1b64efad41caa9a2 100644 (file)
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -465,6 +465,45 @@ build_join_rel(PlannerInfo *root,
        return joinrel;
 }
 
+/*
+ * min_join_parameterization
+ *
+ * Determine the minimum possible parameterization of a joinrel, that is, the
+ * set of other rels it contains LATERAL references to.
+ */
+Relids
+min_join_parameterization(PlannerInfo *root, Relids joinrelids)
+{
+       Relids          result;
+       ListCell   *lc;
+
+       /* Easy if there are no lateral references */
+       if (root->lateral_info_list == NIL)
+               return NULL;
+
+       /*
+        * Scan lateral_info_list to find all the lateral references occurring in
+        * or below this join.
+        */
+       result = NULL;
+       foreach(lc, root->lateral_info_list)
+       {
+               LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(lc);
+
+               if (bms_is_subset(ljinfo->lateral_rhs, joinrelids))
+                       result = bms_add_members(result, ljinfo->lateral_lhs);
+       }
+
+       /* Remove any rels that are already included in the join */
+       result = bms_del_members(result, joinrelids);
+
+       /* Maintain invariant that result is exactly NULL if empty */
+       if (bms_is_empty(result))
+               result = NULL;
+
+       return result;
+}
+
 /*
  * build_joinrel_tlist
  *       Builds a join relation's target list from an input relation.

diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 26b17f5f7afcfcbcaa5c9b9aae4603b37128e2f3..fe06eb1f617a80056f94601d5173667c54b0c6a0 100644 (file)
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -142,6 +142,7 @@ extern RelOptInfo *build_join_rel(PlannerInfo *root,
                           RelOptInfo *inner_rel,
                           SpecialJoinInfo *sjinfo,
                           List **restrictlist_ptr);
+extern Relids min_join_parameterization(PlannerInfo *root, Relids joinrelids);
 extern RelOptInfo *build_empty_join_rel(PlannerInfo *root);
 extern AppendRelInfo *find_childrel_appendrelinfo(PlannerInfo *root,
                                                        RelOptInfo *rel);

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 23198fbe34f1fde65832754bc90da59fd8e241b1..9c6ab9b65f3d9ecff70d6ac5b16c96e239e1e60a 100644 (file)
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3539,6 +3539,47 @@ select * from
  doh! | 123 | 456 | hi de ho neighbor |   
 (2 rows)
 
+--
+-- test for appropriate join order in the presence of lateral references
+--
+explain (verbose, costs off)
+select * from
+  text_tbl t1
+  left join int8_tbl i8
+  on i8.q2 = 123,
+  lateral (select i8.q1, t2.f1 from text_tbl t2 limit 1) as ss
+where t1.f1 = ss.f1;
+                    QUERY PLAN                    
+--------------------------------------------------
+ Nested Loop
+   Output: t1.f1, i8.q1, i8.q2, (i8.q1), t2.f1
+   Join Filter: (t1.f1 = t2.f1)
+   ->  Nested Loop Left Join
+         Output: t1.f1, i8.q1, i8.q2
+         ->  Seq Scan on public.text_tbl t1
+               Output: t1.f1
+         ->  Materialize
+               Output: i8.q1, i8.q2
+               ->  Seq Scan on public.int8_tbl i8
+                     Output: i8.q1, i8.q2
+                     Filter: (i8.q2 = 123)
+   ->  Limit
+         Output: (i8.q1), t2.f1
+         ->  Seq Scan on public.text_tbl t2
+               Output: i8.q1, t2.f1
+(16 rows)
+
+select * from
+  text_tbl t1
+  left join int8_tbl i8
+  on i8.q2 = 123,
+  lateral (select i8.q1, t2.f1 from text_tbl t2 limit 1) as ss
+where t1.f1 = ss.f1;
+  f1  |        q1        | q2  |        q1        |  f1  
+------+------------------+-----+------------------+------
+ doh! | 4567890123456789 | 123 | 4567890123456789 | doh!
+(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 2e17a8b87630360a396196da1f2552bf24084cbf..1775176b26bd6dbe456739c6a68a81121a9adfea 100644 (file)
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -1099,6 +1099,25 @@ select * from
   left join int4_tbl i4
   on i8.q1 = i4.f1;
 
+--
+-- test for appropriate join order in the presence of lateral references
+--
+
+explain (verbose, costs off)
+select * from
+  text_tbl t1
+  left join int8_tbl i8
+  on i8.q2 = 123,
+  lateral (select i8.q1, t2.f1 from text_tbl t2 limit 1) as ss
+where t1.f1 = ss.f1;
+
+select * from
+  text_tbl t1
+  left join int8_tbl i8
+  on i8.q2 = 123,
+  lateral (select i8.q1, t2.f1 from text_tbl t2 limit 1) as ss
+where t1.f1 = ss.f1;
+
 --
 -- test ability to push constants through outer join clauses
 --