diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 03be7b1..5777cb2 100644
*** a/src/backend/optimizer/path/allpaths.c
--- b/src/backend/optimizer/path/allpaths.c
*************** get_cheapest_parameterized_child_path(Pl
*** 1021,1030 ****
   * accumulate_append_subpath
   *		Add a subpath to the list being built for an Append or MergeAppend
   *
!  * It's possible that the child is itself an Append path, in which case
!  * we can "cut out the middleman" and just add its child paths to our
!  * own list.  (We don't try to do this earlier because we need to
!  * apply both levels of transformation to the quals.)
   */
  static List *
  accumulate_append_subpath(List *subpaths, Path *path)
--- 1021,1035 ----
   * accumulate_append_subpath
   *		Add a subpath to the list being built for an Append or MergeAppend
   *
!  * It's possible that the child is itself an Append or MergeAppend path, in
!  * which case we can "cut out the middleman" and just add its child paths to
!  * our own list.  (We don't try to do this earlier because we need to apply
!  * both levels of transformation to the quals.)
!  *
!  * Note that if we omit a child MergeAppend in this way, we are effectively
!  * omitting a sort step, which seems fine: if the parent is to be an Append,
!  * its result would be unsorted anyway, while if the parent is to be a
!  * MergeAppend, there's no point in a separate sort on a child.
   */
  static List *
  accumulate_append_subpath(List *subpaths, Path *path)
*************** accumulate_append_subpath(List *subpaths
*** 1036,1041 ****
--- 1041,1053 ----
  		/* list_copy is important here to avoid sharing list substructure */
  		return list_concat(subpaths, list_copy(apath->subpaths));
  	}
+ 	else if (IsA(path, MergeAppendPath))
+ 	{
+ 		MergeAppendPath *mpath = (MergeAppendPath *) path;
+ 
+ 		/* list_copy is important here to avoid sharing list substructure */
+ 		return list_concat(subpaths, list_copy(mpath->subpaths));
+ 	}
  	else
  		return lappend(subpaths, path);
  }
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 35d2a83..ac12f84 100644
*** a/src/backend/optimizer/path/equivclass.c
--- b/src/backend/optimizer/path/equivclass.c
*************** add_child_rel_equivalences(PlannerInfo *
*** 1937,1952 ****
  		if (cur_ec->ec_has_volatile)
  			continue;
  
! 		/* No point in searching if parent rel not mentioned in eclass */
! 		if (!bms_is_subset(parent_rel->relids, cur_ec->ec_relids))
  			continue;
  
  		foreach(lc2, cur_ec->ec_members)
  		{
  			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
  
! 			if (cur_em->em_is_const || cur_em->em_is_child)
! 				continue;		/* ignore consts and children here */
  
  			/* Does it reference parent_rel? */
  			if (bms_overlap(cur_em->em_relids, parent_rel->relids))
--- 1937,1956 ----
  		if (cur_ec->ec_has_volatile)
  			continue;
  
! 		/*
! 		 * No point in searching if parent rel not mentioned in eclass; but
! 		 * we can't tell that for sure if parent rel is itself a child.
! 		 */
! 		if (parent_rel->reloptkind == RELOPT_BASEREL &&
! 			!bms_is_subset(parent_rel->relids, cur_ec->ec_relids))
  			continue;
  
  		foreach(lc2, cur_ec->ec_members)
  		{
  			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
  
! 			if (cur_em->em_is_const)
! 				continue;		/* ignore consts here */
  
  			/* Does it reference parent_rel? */
  			if (bms_overlap(cur_em->em_relids, parent_rel->relids))
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 184d37a..784805f 100644
*** a/src/backend/optimizer/plan/createplan.c
--- b/src/backend/optimizer/plan/createplan.c
*************** create_merge_append_plan(PlannerInfo *ro
*** 751,757 ****
  
  	/* Compute sort column info, and adjust MergeAppend's tlist as needed */
  	(void) prepare_sort_from_pathkeys(root, plan, pathkeys,
! 									  NULL,
  									  NULL,
  									  true,
  									  &node->numCols,
--- 751,757 ----
  
  	/* Compute sort column info, and adjust MergeAppend's tlist as needed */
  	(void) prepare_sort_from_pathkeys(root, plan, pathkeys,
! 									  best_path->path.parent->relids,
  									  NULL,
  									  true,
  									  &node->numCols,