Fix some new issues with planning of PlaceHolderVars.

In the wake of commit a16ef313f, we need to deal with more cases
involving PlaceHolderVars in NestLoopParams than we did before.

For one thing, a16ef313f was incorrect to suppose that we could
rely on the required-outer relids of the lefthand path to decide
placement of nestloop-parameter PHVs.  As Richard Guo argued at
the time, we must look at the required-outer relids of the join
path itself.

For another, we have to apply replace_nestloop_params() to such
a PHV's expression, in case it contains references to values that
will be supplied from NestLoopParams of higher-level nestloops.

For another, we need to be more careful about the phnullingrels
of the PHV than we were being.  identify_current_nestloop_params
only bothered to ensure that the phnullingrels didn't contain
"too many" relids, but now it has to be exact, because setrefs.c
will apply both NRM_SUBSET and NRM_SUPERSET checks in different
places.  We can compute the correct relids by determining the
set of outer joins that should be able to null the PHV and then
subtracting whatever's been applied at or below this join.
Do the same for plain Vars, too.  (This should make it possible
to use NRM_EQUAL to process nestloop params in setrefs.c, but
I won't risk making such a change in v18 now.)

Lastly, if a nestloop parameter PHV was pulled up out of a subquery
and it contains a subquery that was originally pushed down from this
query level, then that will still be represented as a SubLink, because
SS_process_sublinks won't recurse into outer PHVs, so it didn't get
transformed during expression preprocessing in the subquery.  We can
substitute the version of the PHV's expression appearing in its
PlaceHolderInfo to ensure that that preprocessing has happened.
(Seems like this processing sequence could stand to be redesigned,
but again, late in v18 development is not the time for that.)

It's not very clear to me why the old have_dangerous_phv join-order
restriction prevented us from seeing the last three of these problems.
But given the lack of field complaints, it must have done so.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/18953-1c9883a9d4afeb30@postgresql.org

2 files changed, 204 insertions, 0 deletions

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index c292f04fdba..390aabfb34b 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -4119,6 +4119,164 @@ select * from int8_tbl t1
 (16 rows)
 
 rollback;
+-- ... not that the initial replacement didn't have some bugs too
+begin;
+create temp table t(i int primary key);
+explain (verbose, costs off)
+select * from t t1
+    left join (select 1 as x, * from t t2(i2)) t2ss on t1.i = t2ss.i2
+    left join t t3(i3) on false
+    left join t t4(i4) on t4.i4 > t2ss.x;
+                        QUERY PLAN                        
+----------------------------------------------------------
+ Nested Loop Left Join
+   Output: t1.i, (1), t2.i2, i3, t4.i4
+   ->  Nested Loop Left Join
+         Output: t1.i, t2.i2, (1), i3
+         Join Filter: false
+         ->  Hash Left Join
+               Output: t1.i, t2.i2, (1)
+               Inner Unique: true
+               Hash Cond: (t1.i = t2.i2)
+               ->  Seq Scan on pg_temp.t t1
+                     Output: t1.i
+               ->  Hash
+                     Output: t2.i2, (1)
+                     ->  Seq Scan on pg_temp.t t2
+                           Output: t2.i2, 1
+         ->  Result
+               Output: i3
+               One-Time Filter: false
+   ->  Memoize
+         Output: t4.i4
+         Cache Key: (1)
+         Cache Mode: binary
+         ->  Index Only Scan using t_pkey on pg_temp.t t4
+               Output: t4.i4
+               Index Cond: (t4.i4 > (1))
+(25 rows)
+
+explain (verbose, costs off)
+select * from
+     (select k from
+         (select i, coalesce(i, j) as k from
+             (select i from t union all select 0)
+             join (select 1 as j limit 1) on i = j)
+         right join (select 2 as x) on true
+         join (select 3 as y) on i is not null
+     ),
+     lateral (select k as kl limit 1);
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Nested Loop
+   Output: COALESCE(t.i, (1)), ((COALESCE(t.i, (1))))
+   ->  Limit
+         Output: 1
+         ->  Result
+               Output: 1
+   ->  Nested Loop
+         Output: t.i, ((COALESCE(t.i, (1))))
+         ->  Result
+               Output: t.i, COALESCE(t.i, (1))
+               ->  Append
+                     ->  Index Only Scan using t_pkey on pg_temp.t
+                           Output: t.i
+                           Index Cond: (t.i = (1))
+                     ->  Result
+                           Output: 0
+                           One-Time Filter: ((1) = 0)
+         ->  Limit
+               Output: ((COALESCE(t.i, (1))))
+               ->  Result
+                     Output: (COALESCE(t.i, (1)))
+(21 rows)
+
+rollback;
+-- PHVs containing SubLinks are quite tricky to get right
+explain (verbose, costs off)
+select *
+from int8_tbl i8
+  inner join
+    (select (select true) as x
+       from int4_tbl i4, lateral (select i4.f1 as y limit 1) ss1
+       where i4.f1 = 0) ss2 on true
+  right join (select false as z) ss3 on true,
+  lateral (select i8.q2 as q2l where x limit 1) ss4
+where i8.q2 = 123;
+                           QUERY PLAN                           
+----------------------------------------------------------------
+ Nested Loop
+   Output: i8.q1, i8.q2, (InitPlan 1).col1, false, (i8.q2)
+   InitPlan 1
+     ->  Result
+           Output: true
+   InitPlan 2
+     ->  Result
+           Output: true
+   ->  Seq Scan on public.int4_tbl i4
+         Output: i4.f1
+         Filter: (i4.f1 = 0)
+   ->  Nested Loop
+         Output: i8.q1, i8.q2, (i8.q2)
+         ->  Subquery Scan on ss1
+               Output: ss1.y, (InitPlan 1).col1
+               ->  Limit
+                     Output: NULL::integer
+                     ->  Result
+                           Output: NULL::integer
+         ->  Nested Loop
+               Output: i8.q1, i8.q2, (i8.q2)
+               ->  Seq Scan on public.int8_tbl i8
+                     Output: i8.q1, i8.q2
+                     Filter: (i8.q2 = 123)
+               ->  Limit
+                     Output: (i8.q2)
+                     ->  Result
+                           Output: i8.q2
+                           One-Time Filter: ((InitPlan 1).col1)
+(29 rows)
+
+explain (verbose, costs off)
+select *
+from int8_tbl i8
+  inner join
+    (select (select true) as x
+       from int4_tbl i4, lateral (select 1 as y limit 1) ss1
+       where i4.f1 = 0) ss2 on true
+  right join (select false as z) ss3 on true,
+  lateral (select i8.q2 as q2l where x limit 1) ss4
+where i8.q2 = 123;
+                           QUERY PLAN                           
+----------------------------------------------------------------
+ Nested Loop
+   Output: i8.q1, i8.q2, (InitPlan 1).col1, false, (i8.q2)
+   InitPlan 1
+     ->  Result
+           Output: true
+   InitPlan 2
+     ->  Result
+           Output: true
+   ->  Limit
+         Output: NULL::integer
+         ->  Result
+               Output: NULL::integer
+   ->  Nested Loop
+         Output: i8.q1, i8.q2, (i8.q2)
+         ->  Seq Scan on public.int4_tbl i4
+               Output: i4.f1, (InitPlan 1).col1
+               Filter: (i4.f1 = 0)
+         ->  Nested Loop
+               Output: i8.q1, i8.q2, (i8.q2)
+               ->  Seq Scan on public.int8_tbl i8
+                     Output: i8.q1, i8.q2
+                     Filter: (i8.q2 = 123)
+               ->  Limit
+                     Output: (i8.q2)
+                     ->  Result
+                           Output: i8.q2
+                           One-Time Filter: ((InitPlan 1).col1)
+(27 rows)
+
 -- Test proper handling of appendrel PHVs during useless-RTE removal
 explain (costs off)
 select * from
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 88d2204e447..f6e7070db65 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -1361,6 +1361,52 @@ select * from int8_tbl t1
   on true;
 rollback;
 
+-- ... not that the initial replacement didn't have some bugs too
+begin;
+create temp table t(i int primary key);
+
+explain (verbose, costs off)
+select * from t t1
+    left join (select 1 as x, * from t t2(i2)) t2ss on t1.i = t2ss.i2
+    left join t t3(i3) on false
+    left join t t4(i4) on t4.i4 > t2ss.x;
+
+explain (verbose, costs off)
+select * from
+     (select k from
+         (select i, coalesce(i, j) as k from
+             (select i from t union all select 0)
+             join (select 1 as j limit 1) on i = j)
+         right join (select 2 as x) on true
+         join (select 3 as y) on i is not null
+     ),
+     lateral (select k as kl limit 1);
+
+rollback;
+
+-- PHVs containing SubLinks are quite tricky to get right
+explain (verbose, costs off)
+select *
+from int8_tbl i8
+  inner join
+    (select (select true) as x
+       from int4_tbl i4, lateral (select i4.f1 as y limit 1) ss1
+       where i4.f1 = 0) ss2 on true
+  right join (select false as z) ss3 on true,
+  lateral (select i8.q2 as q2l where x limit 1) ss4
+where i8.q2 = 123;
+
+explain (verbose, costs off)
+select *
+from int8_tbl i8
+  inner join
+    (select (select true) as x
+       from int4_tbl i4, lateral (select 1 as y limit 1) ss1
+       where i4.f1 = 0) ss2 on true
+  right join (select false as z) ss3 on true,
+  lateral (select i8.q2 as q2l where x limit 1) ss4
+where i8.q2 = 123;
+
 -- Test proper handling of appendrel PHVs during useless-RTE removal
 explain (costs off)
 select * from