Make Vars be outer-join-aware.

Traditionally we used the same Var struct to represent the value
of a table column everywhere in parse and plan trees.  This choice
predates our support for SQL outer joins, and it's really a pretty
bad idea with outer joins, because the Var's value can depend on
where it is in the tree: it might go to NULL above an outer join.
So expression nodes that are equal() per equalfuncs.c might not
represent the same value, which is a huge correctness hazard for
the planner.

To improve this, decorate Var nodes with a bitmapset showing
which outer joins (identified by RTE indexes) may have nulled
them at the point in the parse tree where the Var appears.
This allows us to trust that equal() Vars represent the same value.
A certain amount of klugery is still needed to cope with cases
where we re-order two outer joins, but it's possible to make it
work without sacrificing that core principle.  PlaceHolderVars
receive similar decoration for the same reason.

In the planner, we include these outer join bitmapsets into the relids
that an expression is considered to depend on, and in consequence also
add outer-join relids to the relids of join RelOptInfos.  This allows
us to correctly perceive whether an expression can be calculated above
or below a particular outer join.

This change affects FDWs that want to plan foreign joins.  They *must*
follow suit when labeling foreign joins in order to match with the
core planner, but for many purposes (if postgres_fdw is any guide)
they'd prefer to consider only base relations within the join.
To support both requirements, redefine ForeignScan.fs_relids as
base+OJ relids, and add a new field fs_base_relids that's set up by
the core planner.

Large though it is, this commit just does the minimum necessary to
install the new mechanisms and get check-world passing again.
Follow-up patches will perform some cleanup.  (The README additions
and comments mention some stuff that will appear in the follow-up.)

Patch by me; thanks to Richard Guo for review.

Discussion: https://postgr.es/m/830269.1656693747@sss.pgh.pa.us

1 files changed, 157 insertions, 6 deletions

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index c2b85d2795..51c9df3d58 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -2335,17 +2335,17 @@ select a.f1, b.f1, t.thousand, t.tenthous from
   (select sum(f1)+1 as f1 from int4_tbl i4a) a,
   (select sum(f1) as f1 from int4_tbl i4b) b
 where b.f1 = t.thousand and a.f1 = b.f1 and (a.f1+b.f1+999) = t.tenthous;
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
+                                                   QUERY PLAN                                                    
+-----------------------------------------------------------------------------------------------------------------
  Nested Loop
-   ->  Aggregate
-         ->  Seq Scan on int4_tbl i4b
    ->  Nested Loop
          Join Filter: ((sum(i4b.f1)) = ((sum(i4a.f1) + 1)))
          ->  Aggregate
                ->  Seq Scan on int4_tbl i4a
-         ->  Index Only Scan using tenk1_thous_tenthous on tenk1 t
-               Index Cond: ((thousand = (sum(i4b.f1))) AND (tenthous = ((((sum(i4a.f1) + 1)) + (sum(i4b.f1))) + 999)))
+         ->  Aggregate
+               ->  Seq Scan on int4_tbl i4b
+   ->  Index Only Scan using tenk1_thous_tenthous on tenk1 t
+         Index Cond: ((thousand = (sum(i4b.f1))) AND (tenthous = ((((sum(i4a.f1) + 1)) + (sum(i4b.f1))) + 999)))
 (9 rows)
 
 select a.f1, b.f1, t.thousand, t.tenthous from
@@ -4139,6 +4139,60 @@ using (join_key);
 (2 rows)
 
 --
+-- check handling of a variable-free join alias
+--
+explain (verbose, costs off)
+select * from
+int4_tbl i0 left join
+( (select *, 123 as x from int4_tbl i1) ss1
+  left join
+  (select *, q2 as x from int8_tbl i2) ss2
+  using (x)
+) ss0
+on (i0.f1 = ss0.f1)
+order by i0.f1, x;
+                         QUERY PLAN                          
+-------------------------------------------------------------
+ Sort
+   Output: i0.f1, ('123'::bigint), i1.f1, i2.q1, i2.q2
+   Sort Key: i0.f1, ('123'::bigint)
+   ->  Hash Right Join
+         Output: i0.f1, ('123'::bigint), i1.f1, i2.q1, i2.q2
+         Hash Cond: (i1.f1 = i0.f1)
+         ->  Nested Loop Left Join
+               Output: i1.f1, i2.q1, i2.q2, '123'::bigint
+               ->  Seq Scan on public.int4_tbl i1
+                     Output: i1.f1
+               ->  Materialize
+                     Output: i2.q1, i2.q2
+                     ->  Seq Scan on public.int8_tbl i2
+                           Output: i2.q1, i2.q2
+                           Filter: (123 = i2.q2)
+         ->  Hash
+               Output: i0.f1
+               ->  Seq Scan on public.int4_tbl i0
+                     Output: i0.f1
+(19 rows)
+
+select * from
+int4_tbl i0 left join
+( (select *, 123 as x from int4_tbl i1) ss1
+  left join
+  (select *, q2 as x from int8_tbl i2) ss2
+  using (x)
+) ss0
+on (i0.f1 = ss0.f1)
+order by i0.f1, x;
+     f1      |  x  |     f1      |        q1        | q2  
+-------------+-----+-------------+------------------+-----
+ -2147483647 | 123 | -2147483647 | 4567890123456789 | 123
+     -123456 | 123 |     -123456 | 4567890123456789 | 123
+           0 | 123 |           0 | 4567890123456789 | 123
+      123456 | 123 |      123456 | 4567890123456789 | 123
+  2147483647 | 123 |  2147483647 | 4567890123456789 | 123
+(5 rows)
+
+--
 -- test successful handling of nested outer joins with degenerate join quals
 --
 explain (verbose, costs off)
@@ -4728,6 +4782,103 @@ select a.unique1, b.unique2
 (1 row)
 
 --
+-- test full-join strength reduction
+--
+explain (costs off)
+select a.unique1, b.unique2
+  from onek a full join onek b on a.unique1 = b.unique2
+  where a.unique1 = 42;
+                     QUERY PLAN                     
+----------------------------------------------------
+ Nested Loop Left Join
+   Join Filter: (a.unique1 = b.unique2)
+   ->  Index Only Scan using onek_unique1 on onek a
+         Index Cond: (unique1 = 42)
+   ->  Index Only Scan using onek_unique2 on onek b
+         Index Cond: (unique2 = 42)
+(6 rows)
+
+select a.unique1, b.unique2
+  from onek a full join onek b on a.unique1 = b.unique2
+  where a.unique1 = 42;
+ unique1 | unique2 
+---------+---------
+      42 |      42
+(1 row)
+
+explain (costs off)
+select a.unique1, b.unique2
+  from onek a full join onek b on a.unique1 = b.unique2
+  where b.unique2 = 43;
+                     QUERY PLAN                     
+----------------------------------------------------
+ Nested Loop Left Join
+   Join Filter: (a.unique1 = b.unique2)
+   ->  Index Only Scan using onek_unique2 on onek b
+         Index Cond: (unique2 = 43)
+   ->  Index Only Scan using onek_unique1 on onek a
+         Index Cond: (unique1 = 43)
+(6 rows)
+
+select a.unique1, b.unique2
+  from onek a full join onek b on a.unique1 = b.unique2
+  where b.unique2 = 43;
+ unique1 | unique2 
+---------+---------
+      43 |      43
+(1 row)
+
+explain (costs off)
+select a.unique1, b.unique2
+  from onek a full join onek b on a.unique1 = b.unique2
+  where a.unique1 = 42 and b.unique2 = 42;
+                     QUERY PLAN                     
+----------------------------------------------------
+ Nested Loop
+   ->  Index Only Scan using onek_unique1 on onek a
+         Index Cond: (unique1 = 42)
+   ->  Index Only Scan using onek_unique2 on onek b
+         Index Cond: (unique2 = 42)
+(5 rows)
+
+select a.unique1, b.unique2
+  from onek a full join onek b on a.unique1 = b.unique2
+  where a.unique1 = 42 and b.unique2 = 42;
+ unique1 | unique2 
+---------+---------
+      42 |      42
+(1 row)
+
+--
+-- test result-RTE removal underneath a full join
+--
+explain (costs off)
+select * from
+  (select * from int8_tbl i81 join (values(123,2)) v(v1,v2) on q2=v1) ss1
+full join
+  (select * from (values(456,2)) w(v1,v2) join int8_tbl i82 on q2=v1) ss2
+on true;
+              QUERY PLAN              
+--------------------------------------
+ Merge Full Join
+   ->  Seq Scan on int8_tbl i81
+         Filter: (q2 = 123)
+   ->  Materialize
+         ->  Seq Scan on int8_tbl i82
+               Filter: (q2 = 456)
+(6 rows)
+
+select * from
+  (select * from int8_tbl i81 join (values(123,2)) v(v1,v2) on q2=v1) ss1
+full join
+  (select * from (values(456,2)) w(v1,v2) join int8_tbl i82 on q2=v1) ss2
+on true;
+        q1        | q2  | v1  | v2 | v1  | v2 | q1  | q2  
+------------------+-----+-----+----+-----+----+-----+-----
+ 4567890123456789 | 123 | 123 |  2 | 456 |  2 | 123 | 456
+(1 row)
+
+--
 -- test join removal
 --
 begin;