Rewrite make_outerjoininfo's construction of min_lefthand and min_righthand

sets for outer joins, in the light of bug #3588 and additional thought and
experimentation.  The original methodology was fatally flawed for nests of
more than two outer joins: it got the relationships between adjacent joins
right, but didn't always come to the right conclusions about whether a join
could be interchanged with one two or more levels below it.  This was largely
caused by a mistaken idea that we should use the min_lefthand + min_righthand
sets of a sub-join as the minimum left or right input set of an upper join
when we conclude that the sub-join can't commute with the upper one.  If
there's a still-lower join that the sub-join *can* commute with, this method
led us to think that that one could commute with the topmost join; which it
can't.  Another problem (not directly connected to bug #3588) was that
make_outerjoininfo's processing-order-dependent method for enforcing outer
join identity #3 didn't work right: if we decided that join A could safely
commute with lower join B, we dropped all information about sub-joins under B
that join A could perhaps not safely commute with, because we removed B's
entire min_righthand from A's.

To fix, make an explicit computation of all inner join combinations that occur
below an outer join, and add to that the full syntactic relsets of any lower
outer joins that we determine it can't commute with.  This method gives much
more direct enforcement of the outer join rearrangement identities, and it
turns out not to cost a lot of additional bookkeeping.

Thanks to Richard Harris for the bug report and test case.

src/backend/nodes/copyfuncs.c

@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.380 2007/07/17 05:02:01 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.381 2007/08/31 01:44:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1453,6 +1453,8 @@ _copyOuterJoinInfo(OuterJoinInfo *from)
 
 	COPY_BITMAPSET_FIELD(min_lefthand);
 	COPY_BITMAPSET_FIELD(min_righthand);
+	COPY_BITMAPSET_FIELD(syn_lefthand);
+	COPY_BITMAPSET_FIELD(syn_righthand);
 	COPY_SCALAR_FIELD(is_full_join);
 	COPY_SCALAR_FIELD(lhs_strict);
 	COPY_SCALAR_FIELD(delay_upper_joins);

src/backend/nodes/equalfuncs.c

@@ -18,7 +18,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.311 2007/07/17 05:02:01 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.312 2007/08/31 01:44:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -706,6 +706,8 @@ _equalOuterJoinInfo(OuterJoinInfo *a, OuterJoinInfo *b)
 {
 	COMPARE_BITMAPSET_FIELD(min_lefthand);
 	COMPARE_BITMAPSET_FIELD(min_righthand);
+	COMPARE_BITMAPSET_FIELD(syn_lefthand);
+	COMPARE_BITMAPSET_FIELD(syn_righthand);
 	COMPARE_SCALAR_FIELD(is_full_join);
 	COMPARE_SCALAR_FIELD(lhs_strict);
 	COMPARE_SCALAR_FIELD(delay_upper_joins);

src/backend/nodes/outfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.313 2007/07/17 05:02:01 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.314 2007/08/31 01:44:05 tgl Exp $
  *
  * NOTES
  *	  Every node type that can appear in stored rules' parsetrees *must*
@@ -1471,6 +1471,8 @@ _outOuterJoinInfo(StringInfo str, OuterJoinInfo *node)
 
 	WRITE_BITMAPSET_FIELD(min_lefthand);
 	WRITE_BITMAPSET_FIELD(min_righthand);
+	WRITE_BITMAPSET_FIELD(syn_lefthand);
+	WRITE_BITMAPSET_FIELD(syn_righthand);
 	WRITE_BOOL_FIELD(is_full_join);
 	WRITE_BOOL_FIELD(lhs_strict);
 	WRITE_BOOL_FIELD(delay_upper_joins);

src/include/nodes/relation.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.144 2007/05/31 16:57:34 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.145 2007/08/31 01:44:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1044,6 +1044,11 @@ typedef struct InnerIndexscanInfo
  * It is not valid for either min_lefthand or min_righthand to be empty sets;
  * if they were, this would break the logic that enforces join order.
  *
+ * syn_lefthand and syn_righthand are the sets of base relids that are
+ * syntactically below this outer join.  (These are needed to help compute
+ * min_lefthand and min_righthand for higher joins, but are not used
+ * thereafter.)
+ *
  * delay_upper_joins is set TRUE if we detect a pushed-down clause that has
  * to be evaluated after this join is formed (because it references the RHS).
  * Any outer joins that have such a clause and this join in their RHS cannot
@@ -1061,6 +1066,8 @@ typedef struct OuterJoinInfo
 	NodeTag		type;
 	Relids		min_lefthand;	/* base relids in minimum LHS for join */
 	Relids		min_righthand;	/* base relids in minimum RHS for join */
+	Relids		syn_lefthand;	/* base relids syntactically within LHS */
+	Relids		syn_righthand;	/* base relids syntactically within RHS */
 	bool		is_full_join;	/* it's a FULL OUTER JOIN */
 	bool		lhs_strict;		/* joinclause is strict for some LHS rel */
 	bool		delay_upper_joins;	/* can't commute with upper RHS */

src/test/regress/expected/join.out

@@ -2266,3 +2266,27 @@ select * from tt5,tt6 where tt5.f1 = tt6.f1 and tt5.f1 = tt5.f2 - tt6.f2;
   1 | 10 |  1 |  9
 (1 row)
 
+--
+-- regression test for problems of the sort depicted in bug #3588
+--
+create temp table xx (pkxx int);
+create temp table yy (pkyy int, pkxx int);
+insert into xx values (1);
+insert into xx values (2);
+insert into xx values (3);
+insert into yy values (101, 1);
+insert into yy values (201, 2);
+insert into yy values (301, NULL);
+select yy.pkyy as yy_pkyy, yy.pkxx as yy_pkxx, yya.pkyy as yya_pkyy,
+       xxa.pkxx as xxa_pkxx, xxb.pkxx as xxb_pkxx
+from yy
+     left join (SELECT * FROM yy where pkyy = 101) as yya ON yy.pkyy = yya.pkyy
+     left join xx xxa on yya.pkxx = xxa.pkxx
+     left join xx xxb on coalesce (xxa.pkxx, 1) = xxb.pkxx;
+ yy_pkyy | yy_pkxx | yya_pkyy | xxa_pkxx | xxb_pkxx 
+---------+---------+----------+----------+----------
+     101 |       1 |      101 |        1 |        1
+     201 |       2 |          |          |        1
+     301 |         |          |          |        1
+(3 rows)
+

src/test/regress/expected/join_1.out

@@ -2266,3 +2266,27 @@ select * from tt5,tt6 where tt5.f1 = tt6.f1 and tt5.f1 = tt5.f2 - tt6.f2;
   1 | 10 |  1 |  9
 (1 row)
 
+--
+-- regression test for problems of the sort depicted in bug #3588
+--
+create temp table xx (pkxx int);
+create temp table yy (pkyy int, pkxx int);
+insert into xx values (1);
+insert into xx values (2);
+insert into xx values (3);
+insert into yy values (101, 1);
+insert into yy values (201, 2);
+insert into yy values (301, NULL);
+select yy.pkyy as yy_pkyy, yy.pkxx as yy_pkxx, yya.pkyy as yya_pkyy,
+       xxa.pkxx as xxa_pkxx, xxb.pkxx as xxb_pkxx
+from yy
+     left join (SELECT * FROM yy where pkyy = 101) as yya ON yy.pkyy = yya.pkyy
+     left join xx xxa on yya.pkxx = xxa.pkxx
+     left join xx xxb on coalesce (xxa.pkxx, 1) = xxb.pkxx;
+ yy_pkyy | yy_pkxx | yya_pkyy | xxa_pkxx | xxb_pkxx 
+---------+---------+----------+----------+----------
+     101 |       1 |      101 |        1 |        1
+     201 |       2 |          |          |        1
+     301 |         |          |          |        1
+(3 rows)
+

src/test/regress/sql/join.sql

@@ -440,3 +440,25 @@ insert into tt6 values(1, 2);
 insert into tt6 values(2, 9);
 
 select * from tt5,tt6 where tt5.f1 = tt6.f1 and tt5.f1 = tt5.f2 - tt6.f2;
+
+--
+-- regression test for problems of the sort depicted in bug #3588
+--
+
+create temp table xx (pkxx int);
+create temp table yy (pkyy int, pkxx int);
+
+insert into xx values (1);
+insert into xx values (2);
+insert into xx values (3);
+
+insert into yy values (101, 1);
+insert into yy values (201, 2);
+insert into yy values (301, NULL);
+
+select yy.pkyy as yy_pkyy, yy.pkxx as yy_pkxx, yya.pkyy as yya_pkyy,
+       xxa.pkxx as xxa_pkxx, xxb.pkxx as xxb_pkxx
+from yy
+     left join (SELECT * FROM yy where pkyy = 101) as yya ON yy.pkyy = yya.pkyy
+     left join xx xxa on yya.pkxx = xxa.pkxx
+     left join xx xxb on coalesce (xxa.pkxx, 1) = xxb.pkxx;