diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c index b2cc9f07f5..9f0212fad2 100644 --- 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 996b7fe513..8cc7bd771b 100644 --- a/src/backend/optimizer/util/relnode.c +++ b/src/backend/optimizer/util/relnode.c @@ -499,6 +499,47 @@ 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. We save this value in + * the join's RelOptInfo. This function is split out of build_join_rel() + * because join_is_legal() needs the value to check a prospective join. + */ +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 f28b4e2b06..eea75d0d1e 100644 --- a/src/include/optimizer/pathnode.h +++ b/src/include/optimizer/pathnode.h @@ -147,6 +147,7 @@ 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 f8a9f3f264..dba5d2dbab 100644 --- a/src/test/regress/expected/join.out +++ b/src/test/regress/expected/join.out @@ -3579,6 +3579,47 @@ 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 528e1ef970..fdd4e78cf2 100644 --- a/src/test/regress/sql/join.sql +++ b/src/test/regress/sql/join.sql @@ -1115,6 +1115,25 @@ 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 --