Logo Search packages:      
Sourcecode: postgresql-8.4 version File versions  Download package

prepjointree.c

/*-------------------------------------------------------------------------
 *
 * prepjointree.c
 *      Planner preprocessing for subqueries and join tree manipulation.
 *
 * NOTE: the intended sequence for invoking these operations is
 *          pull_up_sublinks
 *          inline_set_returning_functions
 *          pull_up_subqueries
 *          do expression preprocessing (including flattening JOIN alias vars)
 *          reduce_outer_joins
 *
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.66.2.2 2010/06/21 00:14:54 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_type.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/placeholder.h"
#include "optimizer/prep.h"
#include "optimizer/subselect.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#include "parser/parse_relation.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"


00039 typedef struct pullup_replace_vars_context
{
      PlannerInfo *root;
      List     *targetlist;               /* tlist of subquery being pulled up */
      RangeTblEntry *target_rte;          /* RTE of subquery */
      bool     *outer_hasSubLinks;  /* -> outer query's hasSubLinks */
      int               varno;                        /* varno of subquery */
      bool        need_phvs;              /* do we need PlaceHolderVars? */
      bool        wrap_non_vars;          /* do we need 'em on *all* non-Vars? */
      Node    **rv_cache;                 /* cache for results with PHVs */
} pullup_replace_vars_context;

00051 typedef struct reduce_outer_joins_state
{
      Relids            relids;                 /* base relids within this subtree */
      bool        contains_outer; /* does subtree contain outer join(s)? */
      List     *sub_states;         /* List of states for subtree components */
} reduce_outer_joins_state;

static Node *pull_up_sublinks_jointree_recurse(PlannerInfo *root, Node *jtnode,
                                                  Relids *relids);
static Node *pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node,
                                            Relids available_rels, Node **jtlink);
static Node *pull_up_simple_subquery(PlannerInfo *root, Node *jtnode,
                                    RangeTblEntry *rte,
                                    JoinExpr *lowest_outer_join,
                                    AppendRelInfo *containing_appendrel);
static Node *pull_up_simple_union_all(PlannerInfo *root, Node *jtnode,
                                     RangeTblEntry *rte);
static void pull_up_union_leaf_queries(Node *setOp, PlannerInfo *root,
                                       int parentRTindex, Query *setOpQuery,
                                       int childRToffset);
static void make_setop_translation_list(Query *query, Index newvarno,
                                          List **translated_vars);
static bool is_simple_subquery(Query *subquery);
static bool is_simple_union_all(Query *subquery);
static bool is_simple_union_all_recurse(Node *setOp, Query *setOpQuery,
                                          List *colTypes);
static bool is_safe_append_member(Query *subquery);
static void replace_vars_in_jointree(Node *jtnode,
                                     pullup_replace_vars_context *context,
                                     JoinExpr *lowest_outer_join);
static Node *pullup_replace_vars(Node *expr,
                                                 pullup_replace_vars_context *context);
static Node *pullup_replace_vars_callback(Var *var,
                                           replace_rte_variables_context *context);
static reduce_outer_joins_state *reduce_outer_joins_pass1(Node *jtnode);
static void reduce_outer_joins_pass2(Node *jtnode,
                                     reduce_outer_joins_state *state,
                                     PlannerInfo *root,
                                     Relids nonnullable_rels,
                                     List *nonnullable_vars,
                                     List *forced_null_vars);
static void substitute_multiple_relids(Node *node,
                                       int varno, Relids subrelids);
static void fix_append_rel_relids(List *append_rel_list, int varno,
                                Relids subrelids);
static Node *find_jointree_node_for_rel(Node *jtnode, int relid);


/*
 * pull_up_sublinks
 *          Attempt to pull up ANY and EXISTS SubLinks to be treated as
 *          semijoins or anti-semijoins.
 *
 * A clause "foo op ANY (sub-SELECT)" can be processed by pulling the
 * sub-SELECT up to become a rangetable entry and treating the implied
 * comparisons as quals of a semijoin.    However, this optimization *only*
 * works at the top level of WHERE or a JOIN/ON clause, because we cannot
 * distinguish whether the ANY ought to return FALSE or NULL in cases
 * involving NULL inputs.  Also, in an outer join's ON clause we can only
 * do this if the sublink is degenerate (ie, references only the nullable
 * side of the join).  In that case it is legal to push the semijoin
 * down into the nullable side of the join.  If the sublink references any
 * nonnullable-side variables then it would have to be evaluated as part
 * of the outer join, which makes things way too complicated.
 *
 * Under similar conditions, EXISTS and NOT EXISTS clauses can be handled
 * by pulling up the sub-SELECT and creating a semijoin or anti-semijoin.
 *
 * This routine searches for such clauses and does the necessary parsetree
 * transformations if any are found.
 *
 * This routine has to run before preprocess_expression(), so the quals
 * clauses are not yet reduced to implicit-AND format.      That means we need
 * to recursively search through explicit AND clauses, which are
 * probably only binary ANDs.  We stop as soon as we hit a non-AND item.
 */
void
pull_up_sublinks(PlannerInfo *root)
{
      Node     *jtnode;
      Relids            relids;

      /* Begin recursion through the jointree */
      jtnode = pull_up_sublinks_jointree_recurse(root,
                                                                     (Node *) root->parse->jointree,
                                                                     &relids);

      /*
       * root->parse->jointree must always be a FromExpr, so insert a dummy one
       * if we got a bare RangeTblRef or JoinExpr out of the recursion.
       */
      if (IsA(jtnode, FromExpr))
            root->parse->jointree = (FromExpr *) jtnode;
      else
            root->parse->jointree = makeFromExpr(list_make1(jtnode), NULL);
}

/*
 * Recurse through jointree nodes for pull_up_sublinks()
 *
 * In addition to returning the possibly-modified jointree node, we return
 * a relids set of the contained rels into *relids.
 */
static Node *
pull_up_sublinks_jointree_recurse(PlannerInfo *root, Node *jtnode,
                                                  Relids *relids)
{
      if (jtnode == NULL)
      {
            *relids = NULL;
      }
      else if (IsA(jtnode, RangeTblRef))
      {
            int               varno = ((RangeTblRef *) jtnode)->rtindex;

            *relids = bms_make_singleton(varno);
            /* jtnode is returned unmodified */
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            List     *newfromlist = NIL;
            Relids            frelids = NULL;
            FromExpr   *newf;
            Node     *jtlink;
            ListCell   *l;

            /* First, recurse to process children and collect their relids */
            foreach(l, f->fromlist)
            {
                  Node     *newchild;
                  Relids            childrelids;

                  newchild = pull_up_sublinks_jointree_recurse(root,
                                                                                     lfirst(l),
                                                                                     &childrelids);
                  newfromlist = lappend(newfromlist, newchild);
                  frelids = bms_join(frelids, childrelids);
            }
            /* Build the replacement FromExpr; no quals yet */
            newf = makeFromExpr(newfromlist, NULL);
            /* Set up a link representing the rebuilt jointree */
            jtlink = (Node *) newf;
            /* Now process qual --- all children are available for use */
            newf->quals = pull_up_sublinks_qual_recurse(root, f->quals, frelids,
                                                                              &jtlink);

            /*
             * Note that the result will be either newf, or a stack of JoinExprs
             * with newf at the base.  We rely on subsequent optimization steps to
             * flatten this and rearrange the joins as needed.
             *
             * Although we could include the pulled-up subqueries in the returned
             * relids, there's no need since upper quals couldn't refer to their
             * outputs anyway.
             */
            *relids = frelids;
            jtnode = jtlink;
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j;
            Relids            leftrelids;
            Relids            rightrelids;
            Node     *jtlink;

            /*
             * Make a modifiable copy of join node, but don't bother copying its
             * subnodes (yet).
             */
            j = (JoinExpr *) palloc(sizeof(JoinExpr));
            memcpy(j, jtnode, sizeof(JoinExpr));
            jtlink = (Node *) j;

            /* Recurse to process children and collect their relids */
            j->larg = pull_up_sublinks_jointree_recurse(root, j->larg,
                                                                              &leftrelids);
            j->rarg = pull_up_sublinks_jointree_recurse(root, j->rarg,
                                                                              &rightrelids);

            /*
             * Now process qual, showing appropriate child relids as available,
             * and attach any pulled-up jointree items at the right place. In the
             * inner-join case we put new JoinExprs above the existing one (much
             * as for a FromExpr-style join).  In outer-join cases the new
             * JoinExprs must go into the nullable side of the outer join. The
             * point of the available_rels machinations is to ensure that we only
             * pull up quals for which that's okay.
             *
             * XXX for the moment, we refrain from pulling up IN/EXISTS clauses
             * appearing in LEFT or RIGHT join conditions.  Although it is
             * semantically valid to do so under the above conditions, we end up
             * with a query in which the semijoin or antijoin must be evaluated
             * below the outer join, which could perform far worse than leaving it
             * as a sublink that is executed only for row pairs that meet the
             * other join conditions.  Fixing this seems to require considerable
             * restructuring of the executor, but maybe someday it can happen.
             *
             * We don't expect to see any pre-existing JOIN_SEMI or JOIN_ANTI
             * nodes here.
             */
            switch (j->jointype)
            {
                  case JOIN_INNER:
                        j->quals = pull_up_sublinks_qual_recurse(root, j->quals,
                                                                                     bms_union(leftrelids,
                                                                                                rightrelids),
                                                                                     &jtlink);
                        break;
                  case JOIN_LEFT:
#ifdef NOT_USED                           /* see XXX comment above */
                        j->quals = pull_up_sublinks_qual_recurse(root, j->quals,
                                                                                     rightrelids,
                                                                                     &j->rarg);
#endif
                        break;
                  case JOIN_FULL:
                        /* can't do anything with full-join quals */
                        break;
                  case JOIN_RIGHT:
#ifdef NOT_USED                           /* see XXX comment above */
                        j->quals = pull_up_sublinks_qual_recurse(root, j->quals,
                                                                                     leftrelids,
                                                                                     &j->larg);
#endif
                        break;
                  default:
                        elog(ERROR, "unrecognized join type: %d",
                               (int) j->jointype);
                        break;
            }

            /*
             * Although we could include the pulled-up subqueries in the returned
             * relids, there's no need since upper quals couldn't refer to their
             * outputs anyway.      But we *do* need to include the join's own rtindex
             * because we haven't yet collapsed join alias variables, so upper
             * levels would mistakenly think they couldn't use references to this
             * join.
             */
            *relids = bms_join(leftrelids, rightrelids);
            if (j->rtindex)
                  *relids = bms_add_member(*relids, j->rtindex);
            jtnode = jtlink;
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
      return jtnode;
}

/*
 * Recurse through top-level qual nodes for pull_up_sublinks()
 *
 * jtlink points to the link in the jointree where any new JoinExprs should be
 * inserted.  If we find multiple pull-up-able SubLinks, they'll get stacked
 * there in the order we encounter them.  We rely on subsequent optimization
 * to rearrange the stack if appropriate.
 */
static Node *
pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node,
                                            Relids available_rels, Node **jtlink)
{
      if (node == NULL)
            return NULL;
      if (IsA(node, SubLink))
      {
            SubLink    *sublink = (SubLink *) node;
            JoinExpr   *j;

            /* Is it a convertible ANY or EXISTS clause? */
            if (sublink->subLinkType == ANY_SUBLINK)
            {
                  j = convert_ANY_sublink_to_join(root, sublink,
                                                                  available_rels);
                  if (j)
                  {
                        /* Yes, insert the new join node into the join tree */
                        j->larg = *jtlink;
                        *jtlink = (Node *) j;
                        /* and return NULL representing constant TRUE */
                        return NULL;
                  }
            }
            else if (sublink->subLinkType == EXISTS_SUBLINK)
            {
                  j = convert_EXISTS_sublink_to_join(root, sublink, false,
                                                                     available_rels);
                  if (j)
                  {
                        /* Yes, insert the new join node into the join tree */
                        j->larg = *jtlink;
                        *jtlink = (Node *) j;
                        /* and return NULL representing constant TRUE */
                        return NULL;
                  }
            }
            /* Else return it unmodified */
            return node;
      }
      if (not_clause(node))
      {
            /* If the immediate argument of NOT is EXISTS, try to convert */
            SubLink    *sublink = (SubLink *) get_notclausearg((Expr *) node);
            JoinExpr   *j;

            if (sublink && IsA(sublink, SubLink))
            {
                  if (sublink->subLinkType == EXISTS_SUBLINK)
                  {
                        j = convert_EXISTS_sublink_to_join(root, sublink, true,
                                                                           available_rels);
                        if (j)
                        {
                              /* Yes, insert the new join node into the join tree */
                              j->larg = *jtlink;
                              *jtlink = (Node *) j;
                              /* and return NULL representing constant TRUE */
                              return NULL;
                        }
                  }
            }
            /* Else return it unmodified */
            return node;
      }
      if (and_clause(node))
      {
            /* Recurse into AND clause */
            List     *newclauses = NIL;
            ListCell   *l;

            foreach(l, ((BoolExpr *) node)->args)
            {
                  Node     *oldclause = (Node *) lfirst(l);
                  Node     *newclause;

                  newclause = pull_up_sublinks_qual_recurse(root,
                                                                                oldclause,
                                                                                available_rels,
                                                                                jtlink);
                  if (newclause)
                        newclauses = lappend(newclauses, newclause);
            }
            /* We might have got back fewer clauses than we started with */
            if (newclauses == NIL)
                  return NULL;
            else if (list_length(newclauses) == 1)
                  return (Node *) linitial(newclauses);
            else
                  return (Node *) make_andclause(newclauses);
      }
      /* Stop if not an AND */
      return node;
}

/*
 * inline_set_returning_functions
 *          Attempt to "inline" set-returning functions in the FROM clause.
 *
 * If an RTE_FUNCTION rtable entry invokes a set-returning function that
 * contains just a simple SELECT, we can convert the rtable entry to an
 * RTE_SUBQUERY entry exposing the SELECT directly.  This is especially
 * useful if the subquery can then be "pulled up" for further optimization,
 * but we do it even if not, to reduce executor overhead.
 *
 * This has to be done before we have started to do any optimization of
 * subqueries, else any such steps wouldn't get applied to subqueries
 * obtained via inlining.  However, we do it after pull_up_sublinks
 * so that we can inline any functions used in SubLink subselects.
 *
 * Like most of the planner, this feels free to scribble on its input data
 * structure.
 */
void
inline_set_returning_functions(PlannerInfo *root)
{
      ListCell   *rt;

      foreach(rt, root->parse->rtable)
      {
            RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);

            if (rte->rtekind == RTE_FUNCTION)
            {
                  Query    *funcquery;

                  /* Check safety of expansion, and expand if possible */
                  funcquery = inline_set_returning_function(root, rte);
                  if (funcquery)
                  {
                        /* Successful expansion, replace the rtable entry */
                        rte->rtekind = RTE_SUBQUERY;
                        rte->subquery = funcquery;
                        rte->funcexpr = NULL;
                        rte->funccoltypes = NIL;
                        rte->funccoltypmods = NIL;
                  }
            }
      }
}

/*
 * pull_up_subqueries
 *          Look for subqueries in the rangetable that can be pulled up into
 *          the parent query.  If the subquery has no special features like
 *          grouping/aggregation then we can merge it into the parent's jointree.
 *          Also, subqueries that are simple UNION ALL structures can be
 *          converted into "append relations".
 *
 * If this jointree node is within the nullable side of an outer join, then
 * lowest_outer_join references the lowest such JoinExpr node; otherwise it
 * is NULL.  This forces use of the PlaceHolderVar mechanism for references
 * to non-nullable targetlist items, but only for references above that join.
 *
 * If we are looking at a member subquery of an append relation,
 * containing_appendrel describes that relation; else it is NULL.
 * This forces use of the PlaceHolderVar mechanism for all non-Var targetlist
 * items, and puts some additional restrictions on what can be pulled up.
 *
 * A tricky aspect of this code is that if we pull up a subquery we have
 * to replace Vars that reference the subquery's outputs throughout the
 * parent query, including quals attached to jointree nodes above the one
 * we are currently processing!  We handle this by being careful not to
 * change the jointree structure while recursing: no nodes other than
 * subquery RangeTblRef entries will be replaced.  Also, we can't turn
 * pullup_replace_vars loose on the whole jointree, because it'll return a
 * mutated copy of the tree; we have to invoke it just on the quals, instead.
 * This behavior is what makes it reasonable to pass lowest_outer_join as a
 * pointer rather than some more-indirect way of identifying the lowest OJ.
 * Likewise, we don't replace append_rel_list members but only their
 * substructure, so the containing_appendrel reference is safe to use.
 */
Node *
pull_up_subqueries(PlannerInfo *root, Node *jtnode,
                           JoinExpr *lowest_outer_join,
                           AppendRelInfo *containing_appendrel)
{
      if (jtnode == NULL)
            return NULL;
      if (IsA(jtnode, RangeTblRef))
      {
            int               varno = ((RangeTblRef *) jtnode)->rtindex;
            RangeTblEntry *rte = rt_fetch(varno, root->parse->rtable);

            /*
             * Is this a subquery RTE, and if so, is the subquery simple enough to
             * pull up?
             *
             * If we are looking at an append-relation member, we can't pull it up
             * unless is_safe_append_member says so.
             */
            if (rte->rtekind == RTE_SUBQUERY &&
                  is_simple_subquery(rte->subquery) &&
                  (containing_appendrel == NULL ||
                   is_safe_append_member(rte->subquery)))
                  return pull_up_simple_subquery(root, jtnode, rte,
                                                               lowest_outer_join,
                                                               containing_appendrel);

            /*
             * Alternatively, is it a simple UNION ALL subquery?  If so, flatten
             * into an "append relation".
             *
             * It's safe to do this regardless of whether this query is itself an
             * appendrel member.  (If you're thinking we should try to flatten the
             * two levels of appendrel together, you're right; but we handle that
             * in set_append_rel_pathlist, not here.)
             */
            if (rte->rtekind == RTE_SUBQUERY &&
                  is_simple_union_all(rte->subquery))
                  return pull_up_simple_union_all(root, jtnode, rte);

            /* Otherwise, do nothing at this node. */
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            ListCell   *l;

            Assert(containing_appendrel == NULL);
            foreach(l, f->fromlist)
                  lfirst(l) = pull_up_subqueries(root, lfirst(l),
                                                               lowest_outer_join, NULL);
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;

            Assert(containing_appendrel == NULL);
            /* Recurse, being careful to tell myself when inside outer join */
            switch (j->jointype)
            {
                  case JOIN_INNER:
                        j->larg = pull_up_subqueries(root, j->larg,
                                                                   lowest_outer_join, NULL);
                        j->rarg = pull_up_subqueries(root, j->rarg,
                                                                   lowest_outer_join, NULL);
                        break;
                  case JOIN_LEFT:
                  case JOIN_SEMI:
                  case JOIN_ANTI:
                        j->larg = pull_up_subqueries(root, j->larg,
                                                                   lowest_outer_join, NULL);
                        j->rarg = pull_up_subqueries(root, j->rarg,
                                                                   j, NULL);
                        break;
                  case JOIN_FULL:
                        j->larg = pull_up_subqueries(root, j->larg,
                                                                   j, NULL);
                        j->rarg = pull_up_subqueries(root, j->rarg,
                                                                   j, NULL);
                        break;
                  case JOIN_RIGHT:
                        j->larg = pull_up_subqueries(root, j->larg,
                                                                   j, NULL);
                        j->rarg = pull_up_subqueries(root, j->rarg,
                                                                   lowest_outer_join, NULL);
                        break;
                  default:
                        elog(ERROR, "unrecognized join type: %d",
                               (int) j->jointype);
                        break;
            }
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
      return jtnode;
}

/*
 * pull_up_simple_subquery
 *          Attempt to pull up a single simple subquery.
 *
 * jtnode is a RangeTblRef that has been tentatively identified as a simple
 * subquery by pull_up_subqueries.  We return the replacement jointree node,
 * or jtnode itself if we determine that the subquery can't be pulled up after
 * all.
 *
 * rte is the RangeTblEntry referenced by jtnode.  Remaining parameters are
 * as for pull_up_subqueries.
 */
static Node *
pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
                                    JoinExpr *lowest_outer_join,
                                    AppendRelInfo *containing_appendrel)
{
      Query    *parse = root->parse;
      int               varno = ((RangeTblRef *) jtnode)->rtindex;
      Query    *subquery;
      PlannerInfo *subroot;
      int               rtoffset;
      pullup_replace_vars_context rvcontext;
      ListCell   *lc;

      /*
       * Need a modifiable copy of the subquery to hack on.  Even if we didn't
       * sometimes choose not to pull up below, we must do this to avoid
       * problems if the same subquery is referenced from multiple jointree
       * items (which can't happen normally, but might after rule rewriting).
       */
      subquery = copyObject(rte->subquery);

      /*
       * Create a PlannerInfo data structure for this subquery.
       *
       * NOTE: the next few steps should match the first processing in
       * subquery_planner().  Can we refactor to avoid code duplication, or
       * would that just make things uglier?
       */
      subroot = makeNode(PlannerInfo);
      subroot->parse = subquery;
      subroot->glob = root->glob;
      subroot->query_level = root->query_level;
      subroot->parent_root = root->parent_root;
      subroot->planner_cxt = CurrentMemoryContext;
      subroot->init_plans = NIL;
      subroot->cte_plan_ids = NIL;
      subroot->eq_classes = NIL;
      subroot->append_rel_list = NIL;
      subroot->hasRecursion = false;
      subroot->wt_param_id = -1;
      subroot->non_recursive_plan = NULL;

      /* No CTEs to worry about */
      Assert(subquery->cteList == NIL);

      /*
       * Pull up any SubLinks within the subquery's quals, so that we don't
       * leave unoptimized SubLinks behind.
       */
      if (subquery->hasSubLinks)
            pull_up_sublinks(subroot);

      /*
       * Similarly, inline any set-returning functions in its rangetable.
       */
      inline_set_returning_functions(subroot);

      /*
       * Recursively pull up the subquery's subqueries, so that
       * pull_up_subqueries' processing is complete for its jointree and
       * rangetable.
       *
       * Note: we should pass NULL for containing-join info even if we are
       * within an outer join in the upper query; the lower query starts with a
       * clean slate for outer-join semantics.  Likewise, we say we aren't
       * handling an appendrel member.
       */
      subquery->jointree = (FromExpr *)
            pull_up_subqueries(subroot, (Node *) subquery->jointree, NULL, NULL);

      /*
       * Now we must recheck whether the subquery is still simple enough to pull
       * up.      If not, abandon processing it.
       *
       * We don't really need to recheck all the conditions involved, but it's
       * easier just to keep this "if" looking the same as the one in
       * pull_up_subqueries.
       */
      if (is_simple_subquery(subquery) &&
            (containing_appendrel == NULL || is_safe_append_member(subquery)))
      {
            /* good to go */
      }
      else
      {
            /*
             * Give up, return unmodified RangeTblRef.
             *
             * Note: The work we just did will be redone when the subquery gets
             * planned on its own.  Perhaps we could avoid that by storing the
             * modified subquery back into the rangetable, but I'm not gonna risk
             * it now.
             */
            return jtnode;
      }

      /*
       * Adjust level-0 varnos in subquery so that we can append its rangetable
       * to upper query's.  We have to fix the subquery's append_rel_list as
       * well.
       */
      rtoffset = list_length(parse->rtable);
      OffsetVarNodes((Node *) subquery, rtoffset, 0);
      OffsetVarNodes((Node *) subroot->append_rel_list, rtoffset, 0);

      /*
       * Upper-level vars in subquery are now one level closer to their parent
       * than before.
       */
      IncrementVarSublevelsUp((Node *) subquery, -1, 1);
      IncrementVarSublevelsUp((Node *) subroot->append_rel_list, -1, 1);

      /*
       * The subquery's targetlist items are now in the appropriate form to
       * insert into the top query, but if we are under an outer join then
       * non-nullable items may have to be turned into PlaceHolderVars.  If we
       * are dealing with an appendrel member then anything that's not a simple
       * Var has to be turned into a PlaceHolderVar.  Set up appropriate context
       * data for pullup_replace_vars.
       */
      rvcontext.root = root;
      rvcontext.targetlist = subquery->targetList;
      rvcontext.target_rte = rte;
      rvcontext.outer_hasSubLinks = &parse->hasSubLinks;
      rvcontext.varno = varno;
      rvcontext.need_phvs = (lowest_outer_join != NULL ||
                                       containing_appendrel != NULL);
      rvcontext.wrap_non_vars = (containing_appendrel != NULL);
      /* initialize cache array with indexes 0 .. length(tlist) */
      rvcontext.rv_cache = palloc0((list_length(subquery->targetList) + 1) *
                                                 sizeof(Node *));

      /*
       * Replace all of the top query's references to the subquery's outputs
       * with copies of the adjusted subtlist items, being careful not to
       * replace any of the jointree structure. (This'd be a lot cleaner if we
       * could use query_tree_mutator.)  We have to use PHVs in the targetList,
       * returningList, and havingQual, since those are certainly above any
       * outer join.  replace_vars_in_jointree tracks its location in the
       * jointree and uses PHVs or not appropriately.
       */
      parse->targetList = (List *)
            pullup_replace_vars((Node *) parse->targetList, &rvcontext);
      parse->returningList = (List *)
            pullup_replace_vars((Node *) parse->returningList, &rvcontext);
      replace_vars_in_jointree((Node *) parse->jointree, &rvcontext,
                                           lowest_outer_join);
      Assert(parse->setOperations == NULL);
      parse->havingQual = pullup_replace_vars(parse->havingQual, &rvcontext);

      /*
       * Replace references in the translated_vars lists of appendrels. When
       * pulling up an appendrel member, we do not need PHVs in the list of the
       * parent appendrel --- there isn't any outer join between. Elsewhere, use
       * PHVs for safety.  (This analysis could be made tighter but it seems
       * unlikely to be worth much trouble.)
       */
      foreach(lc, root->append_rel_list)
      {
            AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(lc);
            bool  save_need_phvs = rvcontext.need_phvs;

            if (appinfo == containing_appendrel)
                  rvcontext.need_phvs = false;
            appinfo->translated_vars = (List *)
                  pullup_replace_vars((Node *) appinfo->translated_vars, &rvcontext);
            rvcontext.need_phvs = save_need_phvs;
      }

      /*
       * Replace references in the joinaliasvars lists of join RTEs.
       *
       * You might think that we could avoid using PHVs for alias vars of joins
       * below lowest_outer_join, but that doesn't work because the alias vars
       * could be referenced above that join; we need the PHVs to be present in
       * such references after the alias vars get flattened.      (It might be worth
       * trying to be smarter here, someday.)
       */
      foreach(lc, parse->rtable)
      {
            RangeTblEntry *otherrte = (RangeTblEntry *) lfirst(lc);

            if (otherrte->rtekind == RTE_JOIN)
                  otherrte->joinaliasvars = (List *)
                        pullup_replace_vars((Node *) otherrte->joinaliasvars,
                                                      &rvcontext);
      }

      /*
       * Now append the adjusted rtable entries to upper query. (We hold off
       * until after fixing the upper rtable entries; no point in running that
       * code on the subquery ones too.)
       */
      parse->rtable = list_concat(parse->rtable, subquery->rtable);

      /*
       * Pull up any FOR UPDATE/SHARE markers, too.  (OffsetVarNodes already
       * adjusted the marker rtindexes, so just concat the lists.)
       */
      parse->rowMarks = list_concat(parse->rowMarks, subquery->rowMarks);

      /*
       * We also have to fix the relid sets of any PlaceHolderVar nodes in the
       * parent query.  (This could perhaps be done by pullup_replace_vars(),
       * but it seems cleaner to use two passes.)  Note in particular that any
       * PlaceHolderVar nodes just created by pullup_replace_vars()
       * will be adjusted, so having created them with the subquery's varno is
       * correct.
       *
       * Likewise, relids appearing in AppendRelInfo nodes have to be fixed. We
       * already checked that this won't require introducing multiple subrelids
       * into the single-slot AppendRelInfo structs.
       */
      if (parse->hasSubLinks || root->glob->lastPHId != 0 ||
            root->append_rel_list)
      {
            Relids            subrelids;

            subrelids = get_relids_in_jointree((Node *) subquery->jointree, false);
            substitute_multiple_relids((Node *) parse, varno, subrelids);
            fix_append_rel_relids(root->append_rel_list, varno, subrelids);
      }

      /*
       * And now add subquery's AppendRelInfos to our list.
       */
      root->append_rel_list = list_concat(root->append_rel_list,
                                                            subroot->append_rel_list);

      /*
       * We don't have to do the equivalent bookkeeping for outer-join info,
       * because that hasn't been set up yet.  placeholder_list likewise.
       */
      Assert(root->join_info_list == NIL);
      Assert(subroot->join_info_list == NIL);
      Assert(root->placeholder_list == NIL);
      Assert(subroot->placeholder_list == NIL);

      /*
       * Miscellaneous housekeeping.
       *
       * Although replace_rte_variables() faithfully updated parse->hasSubLinks
       * if it copied any SubLinks out of the subquery's targetlist, we still
       * could have SubLinks added to the query in the expressions of FUNCTION
       * and VALUES RTEs copied up from the subquery.  So it's necessary to copy
       * subquery->hasSubLinks anyway.  Perhaps this can be improved someday.
       */
      parse->hasSubLinks |= subquery->hasSubLinks;

      /*
       * subquery won't be pulled up if it hasAggs or hasWindowFuncs, so no work
       * needed on those flags
       */

      /*
       * Return the adjusted subquery jointree to replace the RangeTblRef entry
       * in parent's jointree.
       */
      return (Node *) subquery->jointree;
}

/*
 * pull_up_simple_union_all
 *          Pull up a single simple UNION ALL subquery.
 *
 * jtnode is a RangeTblRef that has been identified as a simple UNION ALL
 * subquery by pull_up_subqueries.  We pull up the leaf subqueries and
 * build an "append relation" for the union set.  The result value is just
 * jtnode, since we don't actually need to change the query jointree.
 */
static Node *
pull_up_simple_union_all(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte)
{
      int               varno = ((RangeTblRef *) jtnode)->rtindex;
      Query    *subquery = rte->subquery;
      int               rtoffset;
      List     *rtable;

      /*
       * Append the subquery rtable entries to upper query.
       */
      rtoffset = list_length(root->parse->rtable);

      /*
       * Append child RTEs to parent rtable.
       *
       * Upper-level vars in subquery are now one level closer to their parent
       * than before.  We don't have to worry about offsetting varnos, though,
       * because any such vars must refer to stuff above the level of the query
       * we are pulling into.
       */
      rtable = copyObject(subquery->rtable);
      IncrementVarSublevelsUp_rtable(rtable, -1, 1);
      root->parse->rtable = list_concat(root->parse->rtable, rtable);

      /*
       * Recursively scan the subquery's setOperations tree and add
       * AppendRelInfo nodes for leaf subqueries to the parent's
       * append_rel_list.
       */
      Assert(subquery->setOperations);
      pull_up_union_leaf_queries(subquery->setOperations, root, varno, subquery,
                                             rtoffset);

      /*
       * Mark the parent as an append relation.
       */
      rte->inh = true;

      return jtnode;
}

/*
 * pull_up_union_leaf_queries -- recursive guts of pull_up_simple_union_all
 *
 * Note that setOpQuery is the Query containing the setOp node, whose rtable
 * is where to look up the RTE if setOp is a RangeTblRef.  This is *not* the
 * same as root->parse, which is the top-level Query we are pulling up into.
 *
 * parentRTindex is the appendrel parent's index in root->parse->rtable.
 *
 * The child RTEs have already been copied to the parent. childRToffset
 * tells us where in the parent's range table they were copied.
 */
static void
pull_up_union_leaf_queries(Node *setOp, PlannerInfo *root, int parentRTindex,
                                       Query *setOpQuery, int childRToffset)
{
      if (IsA(setOp, RangeTblRef))
      {
            RangeTblRef *rtr = (RangeTblRef *) setOp;
            int               childRTindex;
            AppendRelInfo *appinfo;

            /*
             * Calculate the index in the parent's range table
             */
            childRTindex = childRToffset + rtr->rtindex;

            /*
             * Build a suitable AppendRelInfo, and attach to parent's list.
             */
            appinfo = makeNode(AppendRelInfo);
            appinfo->parent_relid = parentRTindex;
            appinfo->child_relid = childRTindex;
            appinfo->parent_reltype = InvalidOid;
            appinfo->child_reltype = InvalidOid;
            make_setop_translation_list(setOpQuery, childRTindex,
                                                      &appinfo->translated_vars);
            appinfo->parent_reloid = InvalidOid;
            root->append_rel_list = lappend(root->append_rel_list, appinfo);

            /*
             * Recursively apply pull_up_subqueries to the new child RTE.  (We
             * must build the AppendRelInfo first, because this will modify it.)
             * Note that we can pass NULL for containing-join info even if we're
             * actually under an outer join, because the child's expressions
             * aren't going to propagate up above the join.
             */
            rtr = makeNode(RangeTblRef);
            rtr->rtindex = childRTindex;
            (void) pull_up_subqueries(root, (Node *) rtr, NULL, appinfo);
      }
      else if (IsA(setOp, SetOperationStmt))
      {
            SetOperationStmt *op = (SetOperationStmt *) setOp;

            /* Recurse to reach leaf queries */
            pull_up_union_leaf_queries(op->larg, root, parentRTindex, setOpQuery,
                                                   childRToffset);
            pull_up_union_leaf_queries(op->rarg, root, parentRTindex, setOpQuery,
                                                   childRToffset);
      }
      else
      {
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(setOp));
      }
}

/*
 * make_setop_translation_list
 *      Build the list of translations from parent Vars to child Vars for
 *      a UNION ALL member.  (At this point it's just a simple list of
 *      referencing Vars, but if we succeed in pulling up the member
 *      subquery, the Vars will get replaced by pulled-up expressions.)
 */
static void
make_setop_translation_list(Query *query, Index newvarno,
                                          List **translated_vars)
{
      List     *vars = NIL;
      ListCell   *l;

      foreach(l, query->targetList)
      {
            TargetEntry *tle = (TargetEntry *) lfirst(l);

            if (tle->resjunk)
                  continue;

            vars = lappend(vars, makeVar(newvarno,
                                                       tle->resno,
                                                       exprType((Node *) tle->expr),
                                                       exprTypmod((Node *) tle->expr),
                                                       0));
      }

      *translated_vars = vars;
}

/*
 * is_simple_subquery
 *      Check a subquery in the range table to see if it's simple enough
 *      to pull up into the parent query.
 */
static bool
is_simple_subquery(Query *subquery)
{
      /*
       * Let's just make sure it's a valid subselect ...
       */
      if (!IsA(subquery, Query) ||
            subquery->commandType != CMD_SELECT ||
            subquery->utilityStmt != NULL ||
            subquery->intoClause != NULL)
            elog(ERROR, "subquery is bogus");

      /*
       * Can't currently pull up a query with setops (unless it's simple UNION
       * ALL, which is handled by a different code path). Maybe after querytree
       * redesign...
       */
      if (subquery->setOperations)
            return false;

      /*
       * Can't pull up a subquery involving grouping, aggregation, sorting,
       * limiting, or WITH.  (XXX WITH could possibly be allowed later)
       */
      if (subquery->hasAggs ||
            subquery->hasWindowFuncs ||
            subquery->groupClause ||
            subquery->havingQual ||
            subquery->sortClause ||
            subquery->distinctClause ||
            subquery->limitOffset ||
            subquery->limitCount ||
            subquery->cteList)
            return false;

      /*
       * Don't pull up a subquery that has any set-returning functions in its
       * targetlist.    Otherwise we might well wind up inserting set-returning
       * functions into places where they mustn't go, such as quals of higher
       * queries.
       */
      if (expression_returns_set((Node *) subquery->targetList))
            return false;

      /*
       * Don't pull up a subquery that has any volatile functions in its
       * targetlist.    Otherwise we might introduce multiple evaluations of these
       * functions, if they get copied to multiple places in the upper query,
       * leading to surprising results.  (Note: the PlaceHolderVar mechanism
       * doesn't quite guarantee single evaluation; else we could pull up anyway
       * and just wrap such items in PlaceHolderVars ...)
       */
      if (contain_volatile_functions((Node *) subquery->targetList))
            return false;

      /*
       * Hack: don't try to pull up a subquery with an empty jointree.
       * query_planner() will correctly generate a Result plan for a jointree
       * that's totally empty, but I don't think the right things happen if an
       * empty FromExpr appears lower down in a jointree.  It would pose a
       * problem for the PlaceHolderVar mechanism too, since we'd have no way to
       * identify where to evaluate a PHV coming out of the subquery. Not worth
       * working hard on this, just to collapse SubqueryScan/Result into Result;
       * especially since the SubqueryScan can often be optimized away by
       * setrefs.c anyway.
       */
      if (subquery->jointree->fromlist == NIL)
            return false;

      return true;
}

/*
 * is_simple_union_all
 *      Check a subquery to see if it's a simple UNION ALL.
 *
 * We require all the setops to be UNION ALL (no mixing) and there can't be
 * any datatype coercions involved, ie, all the leaf queries must emit the
 * same datatypes.
 */
static bool
is_simple_union_all(Query *subquery)
{
      SetOperationStmt *topop;

      /* Let's just make sure it's a valid subselect ... */
      if (!IsA(subquery, Query) ||
            subquery->commandType != CMD_SELECT ||
            subquery->utilityStmt != NULL ||
            subquery->intoClause != NULL)
            elog(ERROR, "subquery is bogus");

      /* Is it a set-operation query at all? */
      topop = (SetOperationStmt *) subquery->setOperations;
      if (!topop)
            return false;
      Assert(IsA(topop, SetOperationStmt));

      /* Can't handle ORDER BY, LIMIT/OFFSET, locking, or WITH */
      if (subquery->sortClause ||
            subquery->limitOffset ||
            subquery->limitCount ||
            subquery->rowMarks ||
            subquery->cteList)
            return false;

      /* Recursively check the tree of set operations */
      return is_simple_union_all_recurse((Node *) topop, subquery,
                                                         topop->colTypes);
}

static bool
is_simple_union_all_recurse(Node *setOp, Query *setOpQuery, List *colTypes)
{
      if (IsA(setOp, RangeTblRef))
      {
            RangeTblRef *rtr = (RangeTblRef *) setOp;
            RangeTblEntry *rte = rt_fetch(rtr->rtindex, setOpQuery->rtable);
            Query    *subquery = rte->subquery;

            Assert(subquery != NULL);

            /* Leaf nodes are OK if they match the toplevel column types */
            /* We don't have to compare typmods here */
            return tlist_same_datatypes(subquery->targetList, colTypes, true);
      }
      else if (IsA(setOp, SetOperationStmt))
      {
            SetOperationStmt *op = (SetOperationStmt *) setOp;

            /* Must be UNION ALL */
            if (op->op != SETOP_UNION || !op->all)
                  return false;

            /* Recurse to check inputs */
            return is_simple_union_all_recurse(op->larg, setOpQuery, colTypes) &&
                  is_simple_union_all_recurse(op->rarg, setOpQuery, colTypes);
      }
      else
      {
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(setOp));
            return false;                 /* keep compiler quiet */
      }
}

/*
 * is_safe_append_member
 *      Check a subquery that is a leaf of a UNION ALL appendrel to see if it's
 *      safe to pull up.
 */
static bool
is_safe_append_member(Query *subquery)
{
      FromExpr   *jtnode;

      /*
       * It's only safe to pull up the child if its jointree contains exactly
       * one RTE, else the AppendRelInfo data structure breaks. The one base RTE
       * could be buried in several levels of FromExpr, however.
       *
       * Also, the child can't have any WHERE quals because there's no place to
       * put them in an appendrel.  (This is a bit annoying...) If we didn't
       * need to check this, we'd just test whether get_relids_in_jointree()
       * yields a singleton set, to be more consistent with the coding of
       * fix_append_rel_relids().
       */
      jtnode = subquery->jointree;
      while (IsA(jtnode, FromExpr))
      {
            if (jtnode->quals != NULL)
                  return false;
            if (list_length(jtnode->fromlist) != 1)
                  return false;
            jtnode = linitial(jtnode->fromlist);
      }
      if (!IsA(jtnode, RangeTblRef))
            return false;

      return true;
}

/*
 * Helper routine for pull_up_subqueries: do pullup_replace_vars on every
 * expression in the jointree, without changing the jointree structure itself.
 * Ugly, but there's no other way...
 *
 * If we are at or below lowest_outer_join, we can suppress use of
 * PlaceHolderVars wrapped around the replacement expressions.
 */
static void
replace_vars_in_jointree(Node *jtnode,
                                     pullup_replace_vars_context *context,
                                     JoinExpr *lowest_outer_join)
{
      if (jtnode == NULL)
            return;
      if (IsA(jtnode, RangeTblRef))
      {
            /* nothing to do here */
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            ListCell   *l;

            foreach(l, f->fromlist)
                  replace_vars_in_jointree(lfirst(l), context, lowest_outer_join);
            f->quals = pullup_replace_vars(f->quals, context);
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;
            bool  save_need_phvs = context->need_phvs;

            if (j == lowest_outer_join)
            {
                  /* no more PHVs in or below this join */
                  context->need_phvs = false;
                  lowest_outer_join = NULL;
            }
            replace_vars_in_jointree(j->larg, context, lowest_outer_join);
            replace_vars_in_jointree(j->rarg, context, lowest_outer_join);
            j->quals = pullup_replace_vars(j->quals, context);

            /*
             * We don't bother to update the colvars list, since it won't be used
             * again ...
             */
            context->need_phvs = save_need_phvs;
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
}

/*
 * Apply pullup variable replacement throughout an expression tree
 *
 * Returns a modified copy of the tree, so this can't be used where we
 * need to do in-place replacement.
 */
static Node *
pullup_replace_vars(Node *expr, pullup_replace_vars_context *context)
{
      return replace_rte_variables(expr,
                                                 context->varno, 0,
                                                 pullup_replace_vars_callback,
                                                 (void *) context,
                                                 context->outer_hasSubLinks);
}

static Node *
pullup_replace_vars_callback(Var *var,
                                           replace_rte_variables_context *context)
{
      pullup_replace_vars_context *rcon = (pullup_replace_vars_context *) context->callback_arg;
      int               varattno = var->varattno;
      Node     *newnode;

      /*
       * If PlaceHolderVars are needed, we cache the modified expressions in
       * rcon->rv_cache[].  This is not in hopes of any material speed gain
       * within this function, but to avoid generating identical PHVs with
       * different IDs.  That would result in duplicate evaluations at runtime,
       * and possibly prevent optimizations that rely on recognizing different
       * references to the same subquery output as being equal().  So it's worth
       * a bit of extra effort to avoid it.
       */
      if (rcon->need_phvs &&
            varattno >= InvalidAttrNumber &&
            varattno <= list_length(rcon->targetlist) &&
            rcon->rv_cache[varattno] != NULL)
      {
            /* Just copy the entry and fall through to adjust its varlevelsup */
            newnode = copyObject(rcon->rv_cache[varattno]);
      }
      else if (varattno == InvalidAttrNumber)
      {
            /* Must expand whole-tuple reference into RowExpr */
            RowExpr    *rowexpr;
            List     *colnames;
            List     *fields;
            bool        save_need_phvs = rcon->need_phvs;
            int               save_sublevelsup = context->sublevels_up;

            /*
             * If generating an expansion for a var of a named rowtype (ie, this
             * is a plain relation RTE), then we must include dummy items for
             * dropped columns.  If the var is RECORD (ie, this is a JOIN), then
             * omit dropped columns. Either way, attach column names to the
             * RowExpr for use of ruleutils.c.
             *
             * In order to be able to cache the results, we always generate the
             * expansion with varlevelsup = 0, and then adjust if needed.
             */
            expandRTE(rcon->target_rte,
                          var->varno, 0 /* not varlevelsup */, var->location,
                          (var->vartype != RECORDOID),
                          &colnames, &fields);
            /* Adjust the generated per-field Vars, but don't insert PHVs */
            rcon->need_phvs = false;
            context->sublevels_up = 0; /* to match the expandRTE output */
            fields = (List *) replace_rte_variables_mutator((Node *) fields,
                                                                                    context);
            rcon->need_phvs = save_need_phvs;
            context->sublevels_up = save_sublevelsup;

            rowexpr = makeNode(RowExpr);
            rowexpr->args = fields;
            rowexpr->row_typeid = var->vartype;
            rowexpr->row_format = COERCE_IMPLICIT_CAST;
            rowexpr->colnames = colnames;
            rowexpr->location = var->location;
            newnode = (Node *) rowexpr;

            /*
             * Insert PlaceHolderVar if needed.  Notice that we are wrapping
             * one PlaceHolderVar around the whole RowExpr, rather than putting
             * one around each element of the row.  This is because we need
             * the expression to yield NULL, not ROW(NULL,NULL,...) when it
             * is forced to null by an outer join.
             */
            if (rcon->need_phvs)
            {
                  /* RowExpr is certainly not strict, so always need PHV */
                  newnode = (Node *)
                        make_placeholder_expr(rcon->root,
                                                        (Expr *) newnode,
                                                        bms_make_singleton(rcon->varno));
                  /* cache it with the PHV, and with varlevelsup still zero */
                  rcon->rv_cache[InvalidAttrNumber] = copyObject(newnode);
            }
      }
      else
      {
            /* Normal case referencing one targetlist element */
            TargetEntry *tle = get_tle_by_resno(rcon->targetlist, varattno);

            if (tle == NULL)        /* shouldn't happen */
                  elog(ERROR, "could not find attribute %d in subquery targetlist",
                         varattno);

            /* Make a copy of the tlist item to return */
            newnode = copyObject(tle->expr);

            /* Insert PlaceHolderVar if needed */
            if (rcon->need_phvs)
            {
                  bool  wrap;

                  if (newnode && IsA(newnode, Var) &&
                        ((Var *) newnode)->varlevelsup == 0)
                  {
                        /* Simple Vars always escape being wrapped */
                        wrap = false;
                  }
                  else if (rcon->wrap_non_vars)
                  {
                        /* Wrap all non-Vars in a PlaceHolderVar */
                        wrap = true;
                  }
                  else
                  {
                        /*
                         * If it contains a Var of current level, and does not contain
                         * any non-strict constructs, then it's certainly nullable and
                         * we don't need to insert a PlaceHolderVar.  (Note: in future
                         * maybe we should insert PlaceHolderVars anyway, when a tlist
                         * item is expensive to evaluate?
                         */
                        if (contain_vars_of_level((Node *) newnode, 0) &&
                              !contain_nonstrict_functions((Node *) newnode))
                        {
                              /* No wrap needed */
                              wrap = false;
                        }
                        else
                        {
                              /* Else wrap it in a PlaceHolderVar */
                              wrap = true;
                        }
                  }

                  if (wrap)
                        newnode = (Node *)
                              make_placeholder_expr(rcon->root,
                                                              (Expr *) newnode,
                                                              bms_make_singleton(rcon->varno));

                  /*
                   * Cache it if possible (ie, if the attno is in range, which it
                   * probably always should be).  We can cache the value even if
                   * we decided we didn't need a PHV, since this result will be
                   * suitable for any request that has need_phvs.
                   */
                  if (varattno > InvalidAttrNumber &&
                        varattno <= list_length(rcon->targetlist))
                        rcon->rv_cache[varattno] = copyObject(newnode);
            }
      }

      /* Must adjust varlevelsup if tlist item is from higher query */
      if (var->varlevelsup > 0)
            IncrementVarSublevelsUp(newnode, var->varlevelsup, 0);

      return newnode;
}

/*
 * reduce_outer_joins
 *          Attempt to reduce outer joins to plain inner joins.
 *
 * The idea here is that given a query like
 *          SELECT ... FROM a LEFT JOIN b ON (...) WHERE b.y = 42;
 * we can reduce the LEFT JOIN to a plain JOIN if the "=" operator in WHERE
 * is strict.  The strict operator will always return NULL, causing the outer
 * WHERE to fail, on any row where the LEFT JOIN filled in NULLs for b's
 * columns.  Therefore, there's no need for the join to produce null-extended
 * rows in the first place --- which makes it a plain join not an outer join.
 * (This scenario may not be very likely in a query written out by hand, but
 * it's reasonably likely when pushing quals down into complex views.)
 *
 * More generally, an outer join can be reduced in strength if there is a
 * strict qual above it in the qual tree that constrains a Var from the
 * nullable side of the join to be non-null.  (For FULL joins this applies
 * to each side separately.)
 *
 * Another transformation we apply here is to recognize cases like
 *          SELECT ... FROM a LEFT JOIN b ON (a.x = b.y) WHERE b.y IS NULL;
 * If the join clause is strict for b.y, then only null-extended rows could
 * pass the upper WHERE, and we can conclude that what the query is really
 * specifying is an anti-semijoin.  We change the join type from JOIN_LEFT
 * to JOIN_ANTI.  The IS NULL clause then becomes redundant, and must be
 * removed to prevent bogus selectivity calculations, but we leave it to
 * distribute_qual_to_rels to get rid of such clauses.
 *
 * Also, we get rid of JOIN_RIGHT cases by flipping them around to become
 * JOIN_LEFT.  This saves some code here and in some later planner routines,
 * but the main reason to do it is to not need to invent a JOIN_REVERSE_ANTI
 * join type.
 *
 * To ease recognition of strict qual clauses, we require this routine to be
 * run after expression preprocessing (i.e., qual canonicalization and JOIN
 * alias-var expansion).
 */
void
reduce_outer_joins(PlannerInfo *root)
{
      reduce_outer_joins_state *state;

      /*
       * To avoid doing strictness checks on more quals than necessary, we want
       * to stop descending the jointree as soon as there are no outer joins
       * below our current point.  This consideration forces a two-pass process.
       * The first pass gathers information about which base rels appear below
       * each side of each join clause, and about whether there are outer
       * join(s) below each side of each join clause. The second pass examines
       * qual clauses and changes join types as it descends the tree.
       */
      state = reduce_outer_joins_pass1((Node *) root->parse->jointree);

      /* planner.c shouldn't have called me if no outer joins */
      if (state == NULL || !state->contains_outer)
            elog(ERROR, "so where are the outer joins?");

      reduce_outer_joins_pass2((Node *) root->parse->jointree,
                                           state, root, NULL, NIL, NIL);
}

/*
 * reduce_outer_joins_pass1 - phase 1 data collection
 *
 * Returns a state node describing the given jointree node.
 */
static reduce_outer_joins_state *
reduce_outer_joins_pass1(Node *jtnode)
{
      reduce_outer_joins_state *result;

      result = (reduce_outer_joins_state *)
            palloc(sizeof(reduce_outer_joins_state));
      result->relids = NULL;
      result->contains_outer = false;
      result->sub_states = NIL;

      if (jtnode == NULL)
            return result;
      if (IsA(jtnode, RangeTblRef))
      {
            int               varno = ((RangeTblRef *) jtnode)->rtindex;

            result->relids = bms_make_singleton(varno);
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            ListCell   *l;

            foreach(l, f->fromlist)
            {
                  reduce_outer_joins_state *sub_state;

                  sub_state = reduce_outer_joins_pass1(lfirst(l));
                  result->relids = bms_add_members(result->relids,
                                                                   sub_state->relids);
                  result->contains_outer |= sub_state->contains_outer;
                  result->sub_states = lappend(result->sub_states, sub_state);
            }
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;
            reduce_outer_joins_state *sub_state;

            /* join's own RT index is not wanted in result->relids */
            if (IS_OUTER_JOIN(j->jointype))
                  result->contains_outer = true;

            sub_state = reduce_outer_joins_pass1(j->larg);
            result->relids = bms_add_members(result->relids,
                                                             sub_state->relids);
            result->contains_outer |= sub_state->contains_outer;
            result->sub_states = lappend(result->sub_states, sub_state);

            sub_state = reduce_outer_joins_pass1(j->rarg);
            result->relids = bms_add_members(result->relids,
                                                             sub_state->relids);
            result->contains_outer |= sub_state->contains_outer;
            result->sub_states = lappend(result->sub_states, sub_state);
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
      return result;
}

/*
 * reduce_outer_joins_pass2 - phase 2 processing
 *
 *    jtnode: current jointree node
 *    state: state data collected by phase 1 for this node
 *    root: toplevel planner state
 *    nonnullable_rels: set of base relids forced non-null by upper quals
 *    nonnullable_vars: list of Vars forced non-null by upper quals
 *    forced_null_vars: list of Vars forced null by upper quals
 */
static void
reduce_outer_joins_pass2(Node *jtnode,
                                     reduce_outer_joins_state *state,
                                     PlannerInfo *root,
                                     Relids nonnullable_rels,
                                     List *nonnullable_vars,
                                     List *forced_null_vars)
{
      /*
       * pass 2 should never descend as far as an empty subnode or base rel,
       * because it's only called on subtrees marked as contains_outer.
       */
      if (jtnode == NULL)
            elog(ERROR, "reached empty jointree");
      if (IsA(jtnode, RangeTblRef))
            elog(ERROR, "reached base rel");
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            ListCell   *l;
            ListCell   *s;
            Relids            pass_nonnullable_rels;
            List     *pass_nonnullable_vars;
            List     *pass_forced_null_vars;

            /* Scan quals to see if we can add any constraints */
            pass_nonnullable_rels = find_nonnullable_rels(f->quals);
            pass_nonnullable_rels = bms_add_members(pass_nonnullable_rels,
                                                                        nonnullable_rels);
            /* NB: we rely on list_concat to not damage its second argument */
            pass_nonnullable_vars = find_nonnullable_vars(f->quals);
            pass_nonnullable_vars = list_concat(pass_nonnullable_vars,
                                                                  nonnullable_vars);
            pass_forced_null_vars = find_forced_null_vars(f->quals);
            pass_forced_null_vars = list_concat(pass_forced_null_vars,
                                                                  forced_null_vars);
            /* And recurse --- but only into interesting subtrees */
            Assert(list_length(f->fromlist) == list_length(state->sub_states));
            forboth(l, f->fromlist, s, state->sub_states)
            {
                  reduce_outer_joins_state *sub_state = lfirst(s);

                  if (sub_state->contains_outer)
                        reduce_outer_joins_pass2(lfirst(l), sub_state, root,
                                                             pass_nonnullable_rels,
                                                             pass_nonnullable_vars,
                                                             pass_forced_null_vars);
            }
            bms_free(pass_nonnullable_rels);
            /* can't so easily clean up var lists, unfortunately */
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;
            int               rtindex = j->rtindex;
            JoinType    jointype = j->jointype;
            reduce_outer_joins_state *left_state = linitial(state->sub_states);
            reduce_outer_joins_state *right_state = lsecond(state->sub_states);
            List     *local_nonnullable_vars = NIL;
            bool        computed_local_nonnullable_vars = false;

            /* Can we simplify this join? */
            switch (jointype)
            {
                  case JOIN_INNER:
                        break;
                  case JOIN_LEFT:
                        if (bms_overlap(nonnullable_rels, right_state->relids))
                              jointype = JOIN_INNER;
                        break;
                  case JOIN_RIGHT:
                        if (bms_overlap(nonnullable_rels, left_state->relids))
                              jointype = JOIN_INNER;
                        break;
                  case JOIN_FULL:
                        if (bms_overlap(nonnullable_rels, left_state->relids))
                        {
                              if (bms_overlap(nonnullable_rels, right_state->relids))
                                    jointype = JOIN_INNER;
                              else
                                    jointype = JOIN_LEFT;
                        }
                        else
                        {
                              if (bms_overlap(nonnullable_rels, right_state->relids))
                                    jointype = JOIN_RIGHT;
                        }
                        break;
                  case JOIN_SEMI:
                  case JOIN_ANTI:

                        /*
                         * These could only have been introduced by pull_up_sublinks,
                         * so there's no way that upper quals could refer to their
                         * righthand sides, and no point in checking.
                         */
                        break;
                  default:
                        elog(ERROR, "unrecognized join type: %d",
                               (int) jointype);
                        break;
            }

            /*
             * Convert JOIN_RIGHT to JOIN_LEFT.  Note that in the case where we
             * reduced JOIN_FULL to JOIN_RIGHT, this will mean the JoinExpr no
             * longer matches the internal ordering of any CoalesceExpr's built to
             * represent merged join variables.  We don't care about that at
             * present, but be wary of it ...
             */
            if (jointype == JOIN_RIGHT)
            {
                  Node     *tmparg;

                  tmparg = j->larg;
                  j->larg = j->rarg;
                  j->rarg = tmparg;
                  jointype = JOIN_LEFT;
                  right_state = linitial(state->sub_states);
                  left_state = lsecond(state->sub_states);
            }

            /*
             * See if we can reduce JOIN_LEFT to JOIN_ANTI.  This is the case if
             * the join's own quals are strict for any var that was forced null by
             * higher qual levels.  NOTE: there are other ways that we could
             * detect an anti-join, in particular if we were to check whether Vars
             * coming from the RHS must be non-null because of table constraints.
             * That seems complicated and expensive though (in particular, one
             * would have to be wary of lower outer joins). For the moment this
             * seems sufficient.
             */
            if (jointype == JOIN_LEFT)
            {
                  List     *overlap;

                  local_nonnullable_vars = find_nonnullable_vars(j->quals);
                  computed_local_nonnullable_vars = true;

                  /*
                   * It's not sufficient to check whether local_nonnullable_vars and
                   * forced_null_vars overlap: we need to know if the overlap
                   * includes any RHS variables.
                   */
                  overlap = list_intersection(local_nonnullable_vars,
                                                            forced_null_vars);
                  if (overlap != NIL &&
                        bms_overlap(pull_varnos((Node *) overlap),
                                          right_state->relids))
                        jointype = JOIN_ANTI;
            }

            /* Apply the jointype change, if any, to both jointree node and RTE */
            if (rtindex && jointype != j->jointype)
            {
                  RangeTblEntry *rte = rt_fetch(rtindex, root->parse->rtable);

                  Assert(rte->rtekind == RTE_JOIN);
                  Assert(rte->jointype == j->jointype);
                  rte->jointype = jointype;
            }
            j->jointype = jointype;

            /* Only recurse if there's more to do below here */
            if (left_state->contains_outer || right_state->contains_outer)
            {
                  Relids            local_nonnullable_rels;
                  List     *local_forced_null_vars;
                  Relids            pass_nonnullable_rels;
                  List     *pass_nonnullable_vars;
                  List     *pass_forced_null_vars;

                  /*
                   * If this join is (now) inner, we can add any constraints its
                   * quals provide to those we got from above.  But if it is outer,
                   * we can pass down the local constraints only into the nullable
                   * side, because an outer join never eliminates any rows from its
                   * non-nullable side.  Also, there is no point in passing upper
                   * constraints into the nullable side, since if there were any
                   * we'd have been able to reduce the join.  (In the case of upper
                   * forced-null constraints, we *must not* pass them into the
                   * nullable side --- they either applied here, or not.) The upshot
                   * is that we pass either the local or the upper constraints,
                   * never both, to the children of an outer join.
                   *
                   * At a FULL join we just punt and pass nothing down --- is it
                   * possible to be smarter?
                   */
                  if (jointype != JOIN_FULL)
                  {
                        local_nonnullable_rels = find_nonnullable_rels(j->quals);
                        if (!computed_local_nonnullable_vars)
                              local_nonnullable_vars = find_nonnullable_vars(j->quals);
                        local_forced_null_vars = find_forced_null_vars(j->quals);
                        if (jointype == JOIN_INNER)
                        {
                              /* OK to merge upper and local constraints */
                              local_nonnullable_rels = bms_add_members(local_nonnullable_rels,
                                                                                       nonnullable_rels);
                              local_nonnullable_vars = list_concat(local_nonnullable_vars,
                                                                                     nonnullable_vars);
                              local_forced_null_vars = list_concat(local_forced_null_vars,
                                                                                     forced_null_vars);
                        }
                  }
                  else
                  {
                        /* no use in calculating these */
                        local_nonnullable_rels = NULL;
                        local_forced_null_vars = NIL;
                  }

                  if (left_state->contains_outer)
                  {
                        if (jointype == JOIN_INNER)
                        {
                              /* pass union of local and upper constraints */
                              pass_nonnullable_rels = local_nonnullable_rels;
                              pass_nonnullable_vars = local_nonnullable_vars;
                              pass_forced_null_vars = local_forced_null_vars;
                        }
                        else if (jointype != JOIN_FULL) /* ie, LEFT/SEMI/ANTI */
                        {
                              /* can't pass local constraints to non-nullable side */
                              pass_nonnullable_rels = nonnullable_rels;
                              pass_nonnullable_vars = nonnullable_vars;
                              pass_forced_null_vars = forced_null_vars;
                        }
                        else
                        {
                              /* no constraints pass through JOIN_FULL */
                              pass_nonnullable_rels = NULL;
                              pass_nonnullable_vars = NIL;
                              pass_forced_null_vars = NIL;
                        }
                        reduce_outer_joins_pass2(j->larg, left_state, root,
                                                             pass_nonnullable_rels,
                                                             pass_nonnullable_vars,
                                                             pass_forced_null_vars);
                  }

                  if (right_state->contains_outer)
                  {
                        if (jointype != JOIN_FULL)          /* ie, INNER/LEFT/SEMI/ANTI */
                        {
                              /* pass appropriate constraints, per comment above */
                              pass_nonnullable_rels = local_nonnullable_rels;
                              pass_nonnullable_vars = local_nonnullable_vars;
                              pass_forced_null_vars = local_forced_null_vars;
                        }
                        else
                        {
                              /* no constraints pass through JOIN_FULL */
                              pass_nonnullable_rels = NULL;
                              pass_nonnullable_vars = NIL;
                              pass_forced_null_vars = NIL;
                        }
                        reduce_outer_joins_pass2(j->rarg, right_state, root,
                                                             pass_nonnullable_rels,
                                                             pass_nonnullable_vars,
                                                             pass_forced_null_vars);
                  }
                  bms_free(local_nonnullable_rels);
            }
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
}

/*
 * substitute_multiple_relids - adjust node relid sets after pulling up
 * a subquery
 *
 * Find any PlaceHolderVar nodes in the given tree that reference the
 * pulled-up relid, and change them to reference the replacement relid(s).
 * We do not need to recurse into subqueries, since no subquery of the current
 * top query could (yet) contain such a reference.
 *
 * NOTE: although this has the form of a walker, we cheat and modify the
 * nodes in-place.  This should be OK since the tree was copied by
 * pullup_replace_vars earlier.  Avoid scribbling on the original values of
 * the bitmapsets, though, because expression_tree_mutator doesn't copy those.
 */

01841 typedef struct
{
      int               varno;
      Relids            subrelids;
} substitute_multiple_relids_context;

static bool
substitute_multiple_relids_walker(Node *node,
                                                  substitute_multiple_relids_context *context)
{
      if (node == NULL)
            return false;
      if (IsA(node, PlaceHolderVar))
      {
            PlaceHolderVar *phv = (PlaceHolderVar *) node;

            if (bms_is_member(context->varno, phv->phrels))
            {
                  phv->phrels = bms_union(phv->phrels,
                                                      context->subrelids);
                  phv->phrels = bms_del_member(phv->phrels,
                                                             context->varno);
            }
            /* fall through to examine children */
      }
      /* Shouldn't need to handle planner auxiliary nodes here */
      Assert(!IsA(node, SpecialJoinInfo));
      Assert(!IsA(node, AppendRelInfo));
      Assert(!IsA(node, PlaceHolderInfo));

      return expression_tree_walker(node, substitute_multiple_relids_walker,
                                                  (void *) context);
}

static void
substitute_multiple_relids(Node *node, int varno, Relids subrelids)
{
      substitute_multiple_relids_context context;

      context.varno = varno;
      context.subrelids = subrelids;

      /*
       * Must be prepared to start with a Query or a bare expression tree.
       */
      query_or_expression_tree_walker(node,
                                                      substitute_multiple_relids_walker,
                                                      (void *) &context,
                                                      0);
}

/*
 * fix_append_rel_relids: update RT-index fields of AppendRelInfo nodes
 *
 * When we pull up a subquery, any AppendRelInfo references to the subquery's
 * RT index have to be replaced by the substituted relid (and there had better
 * be only one).  We also need to apply substitute_multiple_relids to their
 * translated_vars lists, since those might contain PlaceHolderVars.
 *
 * We assume we may modify the AppendRelInfo nodes in-place.
 */
static void
fix_append_rel_relids(List *append_rel_list, int varno, Relids subrelids)
{
      ListCell   *l;
      int               subvarno = -1;

      /*
       * We only want to extract the member relid once, but we mustn't fail
       * immediately if there are multiple members; it could be that none of the
       * AppendRelInfo nodes refer to it.  So compute it on first use. Note that
       * bms_singleton_member will complain if set is not singleton.
       */
      foreach(l, append_rel_list)
      {
            AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);

            /* The parent_relid shouldn't ever be a pullup target */
            Assert(appinfo->parent_relid != varno);

            if (appinfo->child_relid == varno)
            {
                  if (subvarno < 0)
                        subvarno = bms_singleton_member(subrelids);
                  appinfo->child_relid = subvarno;
            }

            /* Also finish fixups for its translated vars */
            substitute_multiple_relids((Node *) appinfo->translated_vars,
                                                   varno, subrelids);
      }
}

/*
 * get_relids_in_jointree: get set of RT indexes present in a jointree
 *
 * If include_joins is true, join RT indexes are included; if false,
 * only base rels are included.
 */
Relids
get_relids_in_jointree(Node *jtnode, bool include_joins)
{
      Relids            result = NULL;

      if (jtnode == NULL)
            return result;
      if (IsA(jtnode, RangeTblRef))
      {
            int               varno = ((RangeTblRef *) jtnode)->rtindex;

            result = bms_make_singleton(varno);
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            ListCell   *l;

            foreach(l, f->fromlist)
            {
                  result = bms_join(result,
                                            get_relids_in_jointree(lfirst(l),
                                                                               include_joins));
            }
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;

            result = get_relids_in_jointree(j->larg, include_joins);
            result = bms_join(result,
                                      get_relids_in_jointree(j->rarg, include_joins));
            if (include_joins && j->rtindex)
                  result = bms_add_member(result, j->rtindex);
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
      return result;
}

/*
 * get_relids_for_join: get set of base RT indexes making up a join
 */
Relids
get_relids_for_join(PlannerInfo *root, int joinrelid)
{
      Node     *jtnode;

      jtnode = find_jointree_node_for_rel((Node *) root->parse->jointree,
                                                            joinrelid);
      if (!jtnode)
            elog(ERROR, "could not find join node %d", joinrelid);
      return get_relids_in_jointree(jtnode, false);
}

/*
 * find_jointree_node_for_rel: locate jointree node for a base or join RT index
 *
 * Returns NULL if not found
 */
static Node *
find_jointree_node_for_rel(Node *jtnode, int relid)
{
      if (jtnode == NULL)
            return NULL;
      if (IsA(jtnode, RangeTblRef))
      {
            int               varno = ((RangeTblRef *) jtnode)->rtindex;

            if (relid == varno)
                  return jtnode;
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            ListCell   *l;

            foreach(l, f->fromlist)
            {
                  jtnode = find_jointree_node_for_rel(lfirst(l), relid);
                  if (jtnode)
                        return jtnode;
            }
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;

            if (relid == j->rtindex)
                  return jtnode;
            jtnode = find_jointree_node_for_rel(j->larg, relid);
            if (jtnode)
                  return jtnode;
            jtnode = find_jointree_node_for_rel(j->rarg, relid);
            if (jtnode)
                  return jtnode;
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
      return NULL;
}

Generated by  Doxygen 1.6.0   Back to index