Fix "cannot handle unplanned sub-select" error that can occur when a

sub-select contains a join alias reference that expands into an expression
containing another sub-select.  Per yesterday's report from Merlin Moncure
and subsequent off-list investigation.

Back-patch to 7.4.  Older versions didn't attempt to flatten sub-selects in
ways that would trigger this problem.

2 files changed, 26 insertions, 0 deletions

diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index b0b260f184..e839ad7f96 100644
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -507,3 +507,17 @@ select (select (a.*)::text) from view_a a;
  (42)
 (1 row)
 
+--
+-- Test case for sublinks pushed down into subselects via join alias expansion
+--
+select
+  (select sq1) as qq1
+from
+  (select exists(select 1 from int4_tbl where f1 = q2) as sq1, 42 as dummy
+   from int8_tbl) sq0
+  join
+  int4_tbl i4 on dummy = i4.f1;
+ qq1 
+-----
+(0 rows)
+
diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index 45be164d1d..f6657fa535 100644
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -323,3 +323,15 @@ select view_a from view_a;
 select (select view_a) from view_a;
 select (select (select view_a)) from view_a;
 select (select (a.*)::text) from view_a a;
+
+--
+-- Test case for sublinks pushed down into subselects via join alias expansion
+--
+
+select
+  (select sq1) as qq1
+from
+  (select exists(select 1 from int4_tbl where f1 = q2) as sq1, 42 as dummy
+   from int8_tbl) sq0
+  join
+  int4_tbl i4 on dummy = i4.f1;