Try to stabilize flappy test result.

This recently-added test case checks the plan of an inner join
between two identical tables.  It's just chance which join order
the planner will pick, and in the presence of any variation in
the underlying statistics, the displayed plan might change.
Add a WHERE condition to break the cost symmetry and hopefully
stabilize matters.

(We're still trying to understand exactly why the underlying
statistics aren't as stable as intended, but this seems like
a good change anyway, since this test would surely bite us
again in future.)

While here, clean up assorted comment spelling, grammar, and
whitespace problems.

Discussion: https://postgr.es/m/4168116.1711720146@sss.pgh.pa.us

Author: tglsfdc

src/test/regress/expected/subselect.out

@@ -1977,7 +1977,7 @@ select * from x for update;
    Output: subselect_tbl.f1, subselect_tbl.f2, subselect_tbl.f3
 (2 rows)
 
--- Pull-up the direct-correlated ANY_SUBLINK
+-- Pull up direct-correlated ANY_SUBLINKs
 explain (costs off)
 select * from tenk1 A where hundred in (select hundred from tenk2 B where B.odd = A.odd);
                          QUERY PLAN                         
@@ -2009,7 +2009,7 @@ WHERE c.odd = b.odd));
 (8 rows)
 
 -- we should only try to pull up the sublink into RHS of a left join
--- but a.hundred is not avaiable.
+-- but a.hundred is not available.
 explain (costs off)
 SELECT * FROM tenk1 A LEFT JOIN tenk2 B
 ON A.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd);
@@ -2026,7 +2026,7 @@ ON A.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd);
 (8 rows)
 
 -- we should only try to pull up the sublink into RHS of a left join
--- but a.odd is not avaiable for this.
+-- but a.odd is not available for this.
 explain (costs off)
 SELECT * FROM tenk1 A LEFT JOIN tenk2 B
 ON B.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = a.odd);
@@ -2042,7 +2042,7 @@ ON B.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = a.odd);
            Filter: (odd = a.odd)
 (8 rows)
 
--- should be able to pull up since all the references is available
+-- should be able to pull up since all the references are available.
 explain (costs off)
 SELECT * FROM tenk1 A LEFT JOIN tenk2 B
 ON B.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd);
@@ -2063,21 +2063,23 @@ ON B.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd);
 -- we can pull up the sublink into the inner JoinExpr.
 explain (costs off)
 SELECT * FROM tenk1 A INNER JOIN tenk2 B
-ON A.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd);
+ON A.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd)
+WHERE a.thousand < 750;
                    QUERY PLAN                    
 -------------------------------------------------
  Hash Join
    Hash Cond: (c.odd = b.odd)
    ->  Hash Join
          Hash Cond: (a.hundred = c.hundred)
          ->  Seq Scan on tenk1 a
+               Filter: (thousand < 750)
          ->  Hash
                ->  HashAggregate
                      Group Key: c.odd, c.hundred
                      ->  Seq Scan on tenk2 c
    ->  Hash
          ->  Seq Scan on tenk2 b
-(11 rows)
+(12 rows)
 
 -- we can pull up the aggregate sublink into RHS of a left join.
 explain (costs off)

src/test/regress/sql/subselect.sql

@@ -983,7 +983,7 @@ explain (verbose, costs off)
 with x as (select * from subselect_tbl)
 select * from x for update;
 
--- Pull-up the direct-correlated ANY_SUBLINK
+-- Pull up direct-correlated ANY_SUBLINKs
 explain (costs off)
 select * from tenk1 A where hundred in (select hundred from tenk2 B where B.odd = A.odd);
 
@@ -994,28 +994,29 @@ where A.hundred in (select C.hundred FROM tenk2 C
 WHERE c.odd = b.odd));
 
 -- we should only try to pull up the sublink into RHS of a left join
--- but a.hundred is not avaiable.
+-- but a.hundred is not available.
 explain (costs off)
 SELECT * FROM tenk1 A LEFT JOIN tenk2 B
 ON A.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd);
 
 -- we should only try to pull up the sublink into RHS of a left join
--- but a.odd is not avaiable for this.
+-- but a.odd is not available for this.
 explain (costs off)
 SELECT * FROM tenk1 A LEFT JOIN tenk2 B
 ON B.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = a.odd);
 
--- should be able to pull up since all the references is available
+-- should be able to pull up since all the references are available.
 explain (costs off)
 SELECT * FROM tenk1 A LEFT JOIN tenk2 B
 ON B.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd);
 
 -- we can pull up the sublink into the inner JoinExpr.
 explain (costs off)
 SELECT * FROM tenk1 A INNER JOIN tenk2 B
-ON A.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd);
+ON A.hundred in (SELECT c.hundred FROM tenk2 C WHERE c.odd = b.odd)
+WHERE a.thousand < 750;
 
 -- we can pull up the aggregate sublink into RHS of a left join.
 explain (costs off)
 SELECT * FROM tenk1 A LEFT JOIN tenk2 B
-ON B.hundred in (SELECT min(c.hundred) FROM tenk2 C WHERE c.odd = b.odd);
+ON B.hundred in (SELECT min(c.hundred) FROM tenk2 C WHERE c.odd = b.odd);