initsplan.c

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/*-------------------------------------------------------------------------
 *
 * initsplan.c
 *    Target list, qualification, joininfo initialization routines
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/plan/initsplan.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_type.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/joininfo.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/placeholder.h"
#include "optimizer/planmain.h"
#include "optimizer/planner.h"
#include "optimizer/prep.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/var.h"
#include "rewrite/rewriteManip.h"
#include "utils/lsyscache.h"


/* These parameters are set by GUC */
int         from_collapse_limit;
int         join_collapse_limit;


static void extract_lateral_references(PlannerInfo *root, RelOptInfo *brel,
                           Index rtindex);
static void add_lateral_info(PlannerInfo *root, Index rhs, Relids lhs);
static List *deconstruct_recurse(PlannerInfo *root, Node *jtnode,
                    bool below_outer_join,
                    Relids *qualscope, Relids *inner_join_rels);
static SpecialJoinInfo *make_outerjoininfo(PlannerInfo *root,
                   Relids left_rels, Relids right_rels,
                   Relids inner_join_rels,
                   JoinType jointype, List *clause);
static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                        bool is_deduced,
                        bool below_outer_join,
                        JoinType jointype,
                        Relids qualscope,
                        Relids ojscope,
                        Relids outerjoin_nonnullable,
                        Relids deduced_nullable_relids);
static bool check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
                      Relids *nullable_relids_p, bool is_pushed_down);
static bool check_equivalence_delay(PlannerInfo *root,
                        RestrictInfo *restrictinfo);
static bool check_redundant_nullability_qual(PlannerInfo *root, Node *clause);
static void check_mergejoinable(RestrictInfo *restrictinfo);
static void check_hashjoinable(RestrictInfo *restrictinfo);


/*****************************************************************************
 *
 *   JOIN TREES
 *
 *****************************************************************************/

/*
 * add_base_rels_to_query
 *
 *    Scan the query's jointree and create baserel RelOptInfos for all
 *    the base relations (ie, table, subquery, and function RTEs)
 *    appearing in the jointree.
 *
 * The initial invocation must pass root->parse->jointree as the value of
 * jtnode.  Internally, the function recurses through the jointree.
 *
 * At the end of this process, there should be one baserel RelOptInfo for
 * every non-join RTE that is used in the query.  Therefore, this routine
 * is the only place that should call build_simple_rel with reloptkind
 * RELOPT_BASEREL.  (Note: build_simple_rel recurses internally to build
 * "other rel" RelOptInfos for the members of any appendrels we find here.)
 */
void
add_base_rels_to_query(PlannerInfo *root, Node *jtnode)
{
    if (jtnode == NULL)
        return;
    if (IsA(jtnode, RangeTblRef))
    {
        int         varno = ((RangeTblRef *) jtnode)->rtindex;

        (void) build_simple_rel(root, varno, RELOPT_BASEREL);
    }
    else if (IsA(jtnode, FromExpr))
    {
        FromExpr   *f = (FromExpr *) jtnode;
        ListCell   *l;

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

        add_base_rels_to_query(root, j->larg);
        add_base_rels_to_query(root, j->rarg);
    }
    else
        elog(ERROR, "unrecognized node type: %d",
             (int) nodeTag(jtnode));
}


/*****************************************************************************
 *
 *   TARGET LISTS
 *
 *****************************************************************************/

/*
 * build_base_rel_tlists
 *    Add targetlist entries for each var needed in the query's final tlist
 *    to the appropriate base relations.
 *
 * We mark such vars as needed by "relation 0" to ensure that they will
 * propagate up through all join plan steps.
 */
void
build_base_rel_tlists(PlannerInfo *root, List *final_tlist)
{
    List       *tlist_vars = pull_var_clause((Node *) final_tlist,
                                             PVC_RECURSE_AGGREGATES,
                                             PVC_INCLUDE_PLACEHOLDERS);

    if (tlist_vars != NIL)
    {
        add_vars_to_targetlist(root, tlist_vars, bms_make_singleton(0), true);
        list_free(tlist_vars);
    }
}

/*
 * add_vars_to_targetlist
 *    For each variable appearing in the list, add it to the owning
 *    relation's targetlist if not already present, and mark the variable
 *    as being needed for the indicated join (or for final output if
 *    where_needed includes "relation 0").
 *
 *    The list may also contain PlaceHolderVars.  These don't necessarily
 *    have a single owning relation; we keep their attr_needed info in
 *    root->placeholder_list instead.  If create_new_ph is true, it's OK
 *    to create new PlaceHolderInfos, and we also have to update ph_may_need;
 *    otherwise, the PlaceHolderInfos must already exist, and we should only
 *    update their ph_needed.  (It should be true before deconstruct_jointree
 *    begins, and false after that.)
 */
void
add_vars_to_targetlist(PlannerInfo *root, List *vars,
                       Relids where_needed, bool create_new_ph)
{
    ListCell   *temp;

    Assert(!bms_is_empty(where_needed));

    foreach(temp, vars)
    {
        Node       *node = (Node *) lfirst(temp);

        if (IsA(node, Var))
        {
            Var        *var = (Var *) node;
            RelOptInfo *rel = find_base_rel(root, var->varno);
            int         attno = var->varattno;

            Assert(attno >= rel->min_attr && attno <= rel->max_attr);
            attno -= rel->min_attr;
            if (rel->attr_needed[attno] == NULL)
            {
                /* Variable not yet requested, so add to reltargetlist */
                /* XXX is copyObject necessary here? */
                rel->reltargetlist = lappend(rel->reltargetlist,
                                             copyObject(var));
            }
            rel->attr_needed[attno] = bms_add_members(rel->attr_needed[attno],
                                                      where_needed);
        }
        else if (IsA(node, PlaceHolderVar))
        {
            PlaceHolderVar *phv = (PlaceHolderVar *) node;
            PlaceHolderInfo *phinfo = find_placeholder_info(root, phv,
                                                            create_new_ph);

            /* Always adjust ph_needed */
            phinfo->ph_needed = bms_add_members(phinfo->ph_needed,
                                                where_needed);

            /*
             * If we are creating PlaceHolderInfos, mark them with the correct
             * maybe-needed locations.  Otherwise, it's too late to change
             * that, so we'd better not have set ph_needed to more than
             * ph_may_need.
             */
            if (create_new_ph)
                mark_placeholder_maybe_needed(root, phinfo, where_needed);
            else
                Assert(bms_is_subset(phinfo->ph_needed, phinfo->ph_may_need));
        }
        else
            elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node));
    }
}


/*****************************************************************************
 *
 *    LATERAL REFERENCES
 *
 *****************************************************************************/

/*
 * find_lateral_references
 *    For each LATERAL subquery, extract all its references to Vars and
 *    PlaceHolderVars of the current query level, and make sure those values
 *    will be available for evaluation of the subquery.
 *
 * While later planning steps ensure that the Var/PHV source rels are on the
 * outside of nestloops relative to the LATERAL subquery, we also need to
 * ensure that the Vars/PHVs propagate up to the nestloop join level; this
 * means setting suitable where_needed values for them.
 *
 * This has to run before deconstruct_jointree, since it might result in
 * creation of PlaceHolderInfos or extension of their ph_may_need sets.
 */
void
find_lateral_references(PlannerInfo *root)
{
    Index       rti;

    /* We need do nothing if the query contains no LATERAL RTEs */
    if (!root->hasLateralRTEs)
        return;

    /*
     * Examine all baserels (the rel array has been set up by now).
     */
    for (rti = 1; rti < root->simple_rel_array_size; rti++)
    {
        RelOptInfo *brel = root->simple_rel_array[rti];

        /* there may be empty slots corresponding to non-baserel RTEs */
        if (brel == NULL)
            continue;

        Assert(brel->relid == rti);     /* sanity check on array */

        /*
         * This bit is less obvious than it might look.  We ignore appendrel
         * otherrels and consider only their parent baserels.  In a case where
         * a LATERAL-containing UNION ALL subquery was pulled up, it is the
         * otherrels that are actually going to be in the plan.  However, we
         * want to mark all their lateral references as needed by the parent,
         * because it is the parent's relid that will be used for join
         * planning purposes.  And the parent's RTE will contain all the
         * lateral references we need to know, since the pulled-up members are
         * nothing but copies of parts of the original RTE's subquery.  We
         * could visit the children instead and transform their references
         * back to the parent's relid, but it would be much more complicated
         * for no real gain.  (Important here is that the child members have
         * not yet received any processing beyond being pulled up.)
         */

        /* ignore RTEs that are "other rels" */
        if (brel->reloptkind != RELOPT_BASEREL)
            continue;

        extract_lateral_references(root, brel, rti);
    }
}

static void
extract_lateral_references(PlannerInfo *root, RelOptInfo *brel, Index rtindex)
{
    RangeTblEntry *rte = root->simple_rte_array[rtindex];
    List       *vars;
    List       *newvars;
    Relids      where_needed;
    ListCell   *lc;

    /* No cross-references are possible if it's not LATERAL */
    if (!rte->lateral)
        return;

    /* Fetch the appropriate variables */
    if (rte->rtekind == RTE_SUBQUERY)
        vars = pull_vars_of_level((Node *) rte->subquery, 1);
    else if (rte->rtekind == RTE_FUNCTION)
        vars = pull_vars_of_level(rte->funcexpr, 0);
    else if (rte->rtekind == RTE_VALUES)
        vars = pull_vars_of_level((Node *) rte->values_lists, 0);
    else
    {
        Assert(false);
        return;                 /* keep compiler quiet */
    }

    if (vars == NIL)
        return;                 /* nothing to do */

    /* Copy each Var (or PlaceHolderVar) and adjust it to match our level */
    newvars = NIL;
    foreach(lc, vars)
    {
        Node   *node = (Node *) lfirst(lc);

        node = copyObject(node);
        if (IsA(node, Var))
        {
            Var    *var = (Var *) node;

            /* Adjustment is easy since it's just one node */
            var->varlevelsup = 0;
        }
        else if (IsA(node, PlaceHolderVar))
        {
            PlaceHolderVar *phv = (PlaceHolderVar *) node;
            int     levelsup = phv->phlevelsup;

            /* Have to work harder to adjust the contained expression too */
            if (levelsup != 0)
                IncrementVarSublevelsUp(node, -levelsup, 0);

            /*
             * If we pulled the PHV out of a subquery RTE, its expression
             * needs to be preprocessed.  subquery_planner() already did this
             * for level-zero PHVs in function and values RTEs, though.
             */
            if (levelsup > 0)
                phv->phexpr = preprocess_phv_expression(root, phv->phexpr);
        }
        else
            Assert(false);
        newvars = lappend(newvars, node);
    }

    list_free(vars);

    /*
     * We mark the Vars as being "needed" at the LATERAL RTE.  This is a bit
     * of a cheat: a more formal approach would be to mark each one as needed
     * at the join of the LATERAL RTE with its source RTE.  But it will work,
     * and it's much less tedious than computing a separate where_needed for
     * each Var.
     */
    where_needed = bms_make_singleton(rtindex);

    /* Push the Vars into their source relations' targetlists */
    add_vars_to_targetlist(root, newvars, where_needed, true);

    /* Remember the lateral references for create_lateral_join_info */
    brel->lateral_vars = newvars;
}

/*
 * create_lateral_join_info
 *    For each LATERAL subquery, create LateralJoinInfo(s) and add them to
 *    root->lateral_info_list, and fill in the per-rel lateral_relids sets.
 *
 * This has to run after deconstruct_jointree, because we need to know the
 * final ph_eval_at values for referenced PlaceHolderVars.
 */
void
create_lateral_join_info(PlannerInfo *root)
{
    Index       rti;

    /* We need do nothing if the query contains no LATERAL RTEs */
    if (!root->hasLateralRTEs)
        return;

    /*
     * Examine all baserels (the rel array has been set up by now).
     */
    for (rti = 1; rti < root->simple_rel_array_size; rti++)
    {
        RelOptInfo *brel = root->simple_rel_array[rti];
        Relids      lateral_relids;
        ListCell *lc;

        /* there may be empty slots corresponding to non-baserel RTEs */
        if (brel == NULL)
            continue;

        Assert(brel->relid == rti);     /* sanity check on array */

        /* ignore RTEs that are "other rels" */
        if (brel->reloptkind != RELOPT_BASEREL)
            continue;

        lateral_relids = NULL;

        /* consider each laterally-referenced Var or PHV */
        foreach(lc, brel->lateral_vars)
        {
            Node   *node = (Node *) lfirst(lc);

            if (IsA(node, Var))
            {
                Var    *var = (Var *) node;

                add_lateral_info(root, rti, bms_make_singleton(var->varno));
                lateral_relids = bms_add_member(lateral_relids,
                                                var->varno);
            }
            else if (IsA(node, PlaceHolderVar))
            {
                PlaceHolderVar *phv = (PlaceHolderVar *) node;
                PlaceHolderInfo *phinfo = find_placeholder_info(root, phv,
                                                                false);

                add_lateral_info(root, rti, bms_copy(phinfo->ph_eval_at));
                lateral_relids = bms_add_members(lateral_relids,
                                                 phinfo->ph_eval_at);
            }
            else
                Assert(false);
        }

        /* We now know all the relids needed for lateral refs in this rel */
        if (bms_is_empty(lateral_relids))
            continue;           /* ensure lateral_relids is NULL if empty */
        brel->lateral_relids = lateral_relids;

        /*
         * If it's an appendrel parent, copy its lateral_relids to each child
         * rel.  We intentionally give each child rel the same minimum
         * parameterization, even though it's quite possible that some don't
         * reference all the lateral rels.  This is because any append path
         * for the parent will have to have the same parameterization for
         * every child anyway, and there's no value in forcing extra
         * reparameterize_path() calls.
         */
        if (root->simple_rte_array[rti]->inh)
        {
            foreach(lc, root->append_rel_list)
            {
                AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(lc);
                RelOptInfo *childrel;

                if (appinfo->parent_relid != rti)
                    continue;
                childrel = root->simple_rel_array[appinfo->child_relid];
                Assert(childrel->reloptkind == RELOPT_OTHER_MEMBER_REL);
                Assert(childrel->lateral_relids == NULL);
                childrel->lateral_relids = lateral_relids;
            }
        }
    }
}

/*
 * add_lateral_info
 *      Add a LateralJoinInfo to root->lateral_info_list, if needed
 *
 * We suppress redundant list entries.  The passed lhs set must be freshly
 * made; we free it if not used in a new list entry.
 */
static void
add_lateral_info(PlannerInfo *root, Index rhs, Relids lhs)
{
    LateralJoinInfo *ljinfo;
    ListCell   *l;

    Assert(!bms_is_member(rhs, lhs));

    /*
     * If an existing list member has the same RHS and an LHS that is a subset
     * of the new one, it's redundant, but we don't trouble to get rid of it.
     * The only case that is really worth worrying about is identical entries,
     * and we handle that well enough with this simple logic.
     */
    foreach(l, root->lateral_info_list)
    {
        ljinfo = (LateralJoinInfo *) lfirst(l);
        if (rhs == ljinfo->lateral_rhs &&
            bms_is_subset(lhs, ljinfo->lateral_lhs))
        {
            bms_free(lhs);
            return;
        }
    }

    /* Not there, so make a new entry */
    ljinfo = makeNode(LateralJoinInfo);
    ljinfo->lateral_rhs = rhs;
    ljinfo->lateral_lhs = lhs;
    root->lateral_info_list = lappend(root->lateral_info_list, ljinfo);
}


/*****************************************************************************
 *
 *    JOIN TREE PROCESSING
 *
 *****************************************************************************/

/*
 * deconstruct_jointree
 *    Recursively scan the query's join tree for WHERE and JOIN/ON qual
 *    clauses, and add these to the appropriate restrictinfo and joininfo
 *    lists belonging to base RelOptInfos.  Also, add SpecialJoinInfo nodes
 *    to root->join_info_list for any outer joins appearing in the query tree.
 *    Return a "joinlist" data structure showing the join order decisions
 *    that need to be made by make_one_rel().
 *
 * The "joinlist" result is a list of items that are either RangeTblRef
 * jointree nodes or sub-joinlists.  All the items at the same level of
 * joinlist must be joined in an order to be determined by make_one_rel()
 * (note that legal orders may be constrained by SpecialJoinInfo nodes).
 * A sub-joinlist represents a subproblem to be planned separately. Currently
 * sub-joinlists arise only from FULL OUTER JOIN or when collapsing of
 * subproblems is stopped by join_collapse_limit or from_collapse_limit.
 *
 * NOTE: when dealing with inner joins, it is appropriate to let a qual clause
 * be evaluated at the lowest level where all the variables it mentions are
 * available.  However, we cannot push a qual down into the nullable side(s)
 * of an outer join since the qual might eliminate matching rows and cause a
 * NULL row to be incorrectly emitted by the join.  Therefore, we artificially
 * OR the minimum-relids of such an outer join into the required_relids of
 * clauses appearing above it.  This forces those clauses to be delayed until
 * application of the outer join (or maybe even higher in the join tree).
 */
List *
deconstruct_jointree(PlannerInfo *root)
{
    Relids      qualscope;
    Relids      inner_join_rels;

    /* Start recursion at top of jointree */
    Assert(root->parse->jointree != NULL &&
           IsA(root->parse->jointree, FromExpr));

    return deconstruct_recurse(root, (Node *) root->parse->jointree, false,
                               &qualscope, &inner_join_rels);
}

/*
 * deconstruct_recurse
 *    One recursion level of deconstruct_jointree processing.
 *
 * Inputs:
 *  jtnode is the jointree node to examine
 *  below_outer_join is TRUE if this node is within the nullable side of a
 *      higher-level outer join
 * Outputs:
 *  *qualscope gets the set of base Relids syntactically included in this
 *      jointree node (do not modify or free this, as it may also be pointed
 *      to by RestrictInfo and SpecialJoinInfo nodes)
 *  *inner_join_rels gets the set of base Relids syntactically included in
 *      inner joins appearing at or below this jointree node (do not modify
 *      or free this, either)
 *  Return value is the appropriate joinlist for this jointree node
 *
 * In addition, entries will be added to root->join_info_list for outer joins.
 */
static List *
deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
                    Relids *qualscope, Relids *inner_join_rels)
{
    List       *joinlist;

    if (jtnode == NULL)
    {
        *qualscope = NULL;
        *inner_join_rels = NULL;
        return NIL;
    }
    if (IsA(jtnode, RangeTblRef))
    {
        int         varno = ((RangeTblRef *) jtnode)->rtindex;

        /* No quals to deal with, just return correct result */
        *qualscope = bms_make_singleton(varno);
        /* A single baserel does not create an inner join */
        *inner_join_rels = NULL;
        joinlist = list_make1(jtnode);
    }
    else if (IsA(jtnode, FromExpr))
    {
        FromExpr   *f = (FromExpr *) jtnode;
        int         remaining;
        ListCell   *l;

        /*
         * First, recurse to handle child joins.  We collapse subproblems into
         * a single joinlist whenever the resulting joinlist wouldn't exceed
         * from_collapse_limit members.  Also, always collapse one-element
         * subproblems, since that won't lengthen the joinlist anyway.
         */
        *qualscope = NULL;
        *inner_join_rels = NULL;
        joinlist = NIL;
        remaining = list_length(f->fromlist);
        foreach(l, f->fromlist)
        {
            Relids      sub_qualscope;
            List       *sub_joinlist;
            int         sub_members;

            sub_joinlist = deconstruct_recurse(root, lfirst(l),
                                               below_outer_join,
                                               &sub_qualscope,
                                               inner_join_rels);
            *qualscope = bms_add_members(*qualscope, sub_qualscope);
            sub_members = list_length(sub_joinlist);
            remaining--;
            if (sub_members <= 1 ||
                list_length(joinlist) + sub_members + remaining <= from_collapse_limit)
                joinlist = list_concat(joinlist, sub_joinlist);
            else
                joinlist = lappend(joinlist, sub_joinlist);
        }

        /*
         * A FROM with more than one list element is an inner join subsuming
         * all below it, so we should report inner_join_rels = qualscope. If
         * there was exactly one element, we should (and already did) report
         * whatever its inner_join_rels were.  If there were no elements (is
         * that possible?) the initialization before the loop fixed it.
         */
        if (list_length(f->fromlist) > 1)
            *inner_join_rels = *qualscope;

        /*
         * Now process the top-level quals.
         */
        foreach(l, (List *) f->quals)
        {
            Node       *qual = (Node *) lfirst(l);

            distribute_qual_to_rels(root, qual,
                                    false, below_outer_join, JOIN_INNER,
                                    *qualscope, NULL, NULL, NULL);
        }
    }
    else if (IsA(jtnode, JoinExpr))
    {
        JoinExpr   *j = (JoinExpr *) jtnode;
        Relids      leftids,
                    rightids,
                    left_inners,
                    right_inners,
                    nonnullable_rels,
                    ojscope;
        List       *leftjoinlist,
                   *rightjoinlist;
        SpecialJoinInfo *sjinfo;
        ListCell   *l;

        /*
         * Order of operations here is subtle and critical.  First we recurse
         * to handle sub-JOINs.  Their join quals will be placed without
         * regard for whether this level is an outer join, which is correct.
         * Then we place our own join quals, which are restricted by lower
         * outer joins in any case, and are forced to this level if this is an
         * outer join and they mention the outer side.  Finally, if this is an
         * outer join, we create a join_info_list entry for the join.  This
         * will prevent quals above us in the join tree that use those rels
         * from being pushed down below this level.  (It's okay for upper
         * quals to be pushed down to the outer side, however.)
         */
        switch (j->jointype)
        {
            case JOIN_INNER:
                leftjoinlist = deconstruct_recurse(root, j->larg,
                                                   below_outer_join,
                                                   &leftids, &left_inners);
                rightjoinlist = deconstruct_recurse(root, j->rarg,
                                                    below_outer_join,
                                                    &rightids, &right_inners);
                *qualscope = bms_union(leftids, rightids);
                *inner_join_rels = *qualscope;
                /* Inner join adds no restrictions for quals */
                nonnullable_rels = NULL;
                break;
            case JOIN_LEFT:
            case JOIN_ANTI:
                leftjoinlist = deconstruct_recurse(root, j->larg,
                                                   below_outer_join,
                                                   &leftids, &left_inners);
                rightjoinlist = deconstruct_recurse(root, j->rarg,
                                                    true,
                                                    &rightids, &right_inners);
                *qualscope = bms_union(leftids, rightids);
                *inner_join_rels = bms_union(left_inners, right_inners);
                nonnullable_rels = leftids;
                break;
            case JOIN_SEMI:
                leftjoinlist = deconstruct_recurse(root, j->larg,
                                                   below_outer_join,
                                                   &leftids, &left_inners);
                rightjoinlist = deconstruct_recurse(root, j->rarg,
                                                    below_outer_join,
                                                    &rightids, &right_inners);
                *qualscope = bms_union(leftids, rightids);
                *inner_join_rels = bms_union(left_inners, right_inners);
                /* Semi join adds no restrictions for quals */
                nonnullable_rels = NULL;
                break;
            case JOIN_FULL:
                leftjoinlist = deconstruct_recurse(root, j->larg,
                                                   true,
                                                   &leftids, &left_inners);
                rightjoinlist = deconstruct_recurse(root, j->rarg,
                                                    true,
                                                    &rightids, &right_inners);
                *qualscope = bms_union(leftids, rightids);
                *inner_join_rels = bms_union(left_inners, right_inners);
                /* each side is both outer and inner */
                nonnullable_rels = *qualscope;
                break;
            default:
                /* JOIN_RIGHT was eliminated during reduce_outer_joins() */
                elog(ERROR, "unrecognized join type: %d",
                     (int) j->jointype);
                nonnullable_rels = NULL;        /* keep compiler quiet */
                leftjoinlist = rightjoinlist = NIL;
                break;
        }

        /*
         * For an OJ, form the SpecialJoinInfo now, because we need the OJ's
         * semantic scope (ojscope) to pass to distribute_qual_to_rels.  But
         * we mustn't add it to join_info_list just yet, because we don't want
         * distribute_qual_to_rels to think it is an outer join below us.
         *
         * Semijoins are a bit of a hybrid: we build a SpecialJoinInfo, but we
         * want ojscope = NULL for distribute_qual_to_rels.
         */
        if (j->jointype != JOIN_INNER)
        {
            sjinfo = make_outerjoininfo(root,
                                        leftids, rightids,
                                        *inner_join_rels,
                                        j->jointype,
                                        (List *) j->quals);
            if (j->jointype == JOIN_SEMI)
                ojscope = NULL;
            else
                ojscope = bms_union(sjinfo->min_lefthand,
                                    sjinfo->min_righthand);
        }
        else
        {
            sjinfo = NULL;
            ojscope = NULL;
        }

        /* Process the qual clauses */
        foreach(l, (List *) j->quals)
        {
            Node       *qual = (Node *) lfirst(l);

            distribute_qual_to_rels(root, qual,
                                    false, below_outer_join, j->jointype,
                                    *qualscope,
                                    ojscope, nonnullable_rels, NULL);
        }

        /* Now we can add the SpecialJoinInfo to join_info_list */
        if (sjinfo)
        {
            root->join_info_list = lappend(root->join_info_list, sjinfo);
            /* Each time we do that, recheck placeholder eval levels */
            update_placeholder_eval_levels(root, sjinfo);
        }

        /*
         * Finally, compute the output joinlist.  We fold subproblems together
         * except at a FULL JOIN or where join_collapse_limit would be
         * exceeded.
         */
        if (j->jointype == JOIN_FULL)
        {
            /* force the join order exactly at this node */
            joinlist = list_make1(list_make2(leftjoinlist, rightjoinlist));
        }
        else if (list_length(leftjoinlist) + list_length(rightjoinlist) <=
                 join_collapse_limit)
        {
            /* OK to combine subproblems */
            joinlist = list_concat(leftjoinlist, rightjoinlist);
        }
        else
        {
            /* can't combine, but needn't force join order above here */
            Node       *leftpart,
                       *rightpart;

            /* avoid creating useless 1-element sublists */
            if (list_length(leftjoinlist) == 1)
                leftpart = (Node *) linitial(leftjoinlist);
            else
                leftpart = (Node *) leftjoinlist;
            if (list_length(rightjoinlist) == 1)
                rightpart = (Node *) linitial(rightjoinlist);
            else
                rightpart = (Node *) rightjoinlist;
            joinlist = list_make2(leftpart, rightpart);
        }
    }
    else
    {
        elog(ERROR, "unrecognized node type: %d",
             (int) nodeTag(jtnode));
        joinlist = NIL;         /* keep compiler quiet */
    }
    return joinlist;
}

/*
 * make_outerjoininfo
 *    Build a SpecialJoinInfo for the current outer join
 *
 * Inputs:
 *  left_rels: the base Relids syntactically on outer side of join
 *  right_rels: the base Relids syntactically on inner side of join
 *  inner_join_rels: base Relids participating in inner joins below this one
 *  jointype: what it says (must always be LEFT, FULL, SEMI, or ANTI)
 *  clause: the outer join's join condition (in implicit-AND format)
 *
 * The node should eventually be appended to root->join_info_list, but we
 * do not do that here.
 *
 * Note: we assume that this function is invoked bottom-up, so that
 * root->join_info_list already contains entries for all outer joins that are
 * syntactically below this one.
 */
static SpecialJoinInfo *
make_outerjoininfo(PlannerInfo *root,
                   Relids left_rels, Relids right_rels,
                   Relids inner_join_rels,
                   JoinType jointype, List *clause)
{
    SpecialJoinInfo *sjinfo = makeNode(SpecialJoinInfo);
    Relids      clause_relids;
    Relids      strict_relids;
    Relids      min_lefthand;
    Relids      min_righthand;
    ListCell   *l;

    /*
     * We should not see RIGHT JOIN here because left/right were switched
     * earlier
     */
    Assert(jointype != JOIN_INNER);
    Assert(jointype != JOIN_RIGHT);

    /*
     * Presently the executor cannot support FOR [KEY] UPDATE/SHARE marking of rels
     * appearing on the nullable side of an outer join. (It's somewhat unclear
     * what that would mean, anyway: what should we mark when a result row is
     * generated from no element of the nullable relation?)  So, complain if
     * any nullable rel is FOR [KEY] UPDATE/SHARE.
     *
     * You might be wondering why this test isn't made far upstream in the
     * parser.  It's because the parser hasn't got enough info --- consider
     * FOR UPDATE applied to a view.  Only after rewriting and flattening do
     * we know whether the view contains an outer join.
     *
     * We use the original RowMarkClause list here; the PlanRowMark list would
     * list everything.
     */
    foreach(l, root->parse->rowMarks)
    {
        RowMarkClause *rc = (RowMarkClause *) lfirst(l);

        if (bms_is_member(rc->rti, right_rels) ||
            (jointype == JOIN_FULL && bms_is_member(rc->rti, left_rels)))
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("row-level locks cannot be applied to the nullable side of an outer join")));
    }

    sjinfo->syn_lefthand = left_rels;
    sjinfo->syn_righthand = right_rels;
    sjinfo->jointype = jointype;
    /* this always starts out false */
    sjinfo->delay_upper_joins = false;
    sjinfo->join_quals = clause;

    /* If it's a full join, no need to be very smart */
    if (jointype == JOIN_FULL)
    {
        sjinfo->min_lefthand = bms_copy(left_rels);
        sjinfo->min_righthand = bms_copy(right_rels);
        sjinfo->lhs_strict = false;     /* don't care about this */
        return sjinfo;
    }

    /*
     * Retrieve all relids mentioned within the join clause.
     */
    clause_relids = pull_varnos((Node *) clause);

    /*
     * For which relids is the clause strict, ie, it cannot succeed if the
     * rel's columns are all NULL?
     */
    strict_relids = find_nonnullable_rels((Node *) clause);

    /* Remember whether the clause is strict for any LHS relations */
    sjinfo->lhs_strict = bms_overlap(strict_relids, left_rels);

    /*
     * Required LHS always includes the LHS rels mentioned in the clause. We
     * may have to add more rels based on lower outer joins; see below.
     */
    min_lefthand = bms_intersect(clause_relids, left_rels);

    /*
     * Similarly for required RHS.  But here, we must also include any lower
     * inner joins, to ensure we don't try to commute with any of them.
     */
    min_righthand = bms_int_members(bms_union(clause_relids, inner_join_rels),
                                    right_rels);

    foreach(l, root->join_info_list)
    {
        SpecialJoinInfo *otherinfo = (SpecialJoinInfo *) lfirst(l);

        /* ignore full joins --- other mechanisms preserve their ordering */
        if (otherinfo->jointype == JOIN_FULL)
            continue;

        /*
         * For a lower OJ in our LHS, if our join condition uses the lower
         * join's RHS and is not strict for that rel, we must preserve the
         * ordering of the two OJs, so add lower OJ's full syntactic relset to
         * min_lefthand.  (We must use its full syntactic relset, not just its
         * min_lefthand + min_righthand.  This is because there might be other
         * OJs below this one that this one can commute with, but we cannot
         * commute with them if we don't with this one.)  Also, if the current
         * join is a semijoin or antijoin, we must preserve ordering
         * regardless of strictness.
         *
         * Note: I believe we have to insist on being strict for at least one
         * rel in the lower OJ's min_righthand, not its whole syn_righthand.
         */
        if (bms_overlap(left_rels, otherinfo->syn_righthand))
        {
            if (bms_overlap(clause_relids, otherinfo->syn_righthand) &&
                (jointype == JOIN_SEMI || jointype == JOIN_ANTI ||
                 !bms_overlap(strict_relids, otherinfo->min_righthand)))
            {
                min_lefthand = bms_add_members(min_lefthand,
                                               otherinfo->syn_lefthand);
                min_lefthand = bms_add_members(min_lefthand,
                                               otherinfo->syn_righthand);
            }
        }

        /*
         * For a lower OJ in our RHS, if our join condition does not use the
         * lower join's RHS and the lower OJ's join condition is strict, we
         * can interchange the ordering of the two OJs; otherwise we must add
         * lower OJ's full syntactic relset to min_righthand.  Here, we must
         * preserve ordering anyway if either the current join is a semijoin,
         * or the lower OJ is either a semijoin or an antijoin.
         *
         * Here, we have to consider that "our join condition" includes any
         * clauses that syntactically appeared above the lower OJ and below
         * ours; those are equivalent to degenerate clauses in our OJ and must
         * be treated as such.  Such clauses obviously can't reference our
         * LHS, and they must be non-strict for the lower OJ's RHS (else
         * reduce_outer_joins would have reduced the lower OJ to a plain
         * join).  Hence the other ways in which we handle clauses within our
         * join condition are not affected by them.  The net effect is
         * therefore sufficiently represented by the delay_upper_joins flag
         * saved for us by check_outerjoin_delay.
         */
        if (bms_overlap(right_rels, otherinfo->syn_righthand))
        {
            if (bms_overlap(clause_relids, otherinfo->syn_righthand) ||
                jointype == JOIN_SEMI ||
                otherinfo->jointype == JOIN_SEMI ||
                otherinfo->jointype == JOIN_ANTI ||
                !otherinfo->lhs_strict || otherinfo->delay_upper_joins)
            {
                min_righthand = bms_add_members(min_righthand,
                                                otherinfo->syn_lefthand);
                min_righthand = bms_add_members(min_righthand,
                                                otherinfo->syn_righthand);
            }
        }
    }

    /*
     * Examine PlaceHolderVars.  If a PHV is supposed to be evaluated within
     * this join's nullable side, and it may get used above this join, then
     * ensure that min_righthand contains the full eval_at set of the PHV.
     * This ensures that the PHV actually can be evaluated within the RHS.
     * Note that this works only because we should already have determined the
     * final eval_at level for any PHV syntactically within this join.
     */
    foreach(l, root->placeholder_list)
    {
        PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
        Relids      ph_syn_level = phinfo->ph_var->phrels;

        /* Ignore placeholder if it didn't syntactically come from RHS */
        if (!bms_is_subset(ph_syn_level, right_rels))
            continue;

        /* We can also ignore it if it's certainly not used above this join */
        /* XXX this test is probably overly conservative */
        if (bms_is_subset(phinfo->ph_may_need, min_righthand))
            continue;

        /* Else, prevent join from being formed before we eval the PHV */
        min_righthand = bms_add_members(min_righthand, phinfo->ph_eval_at);
    }

    /*
     * If we found nothing to put in min_lefthand, punt and make it the full
     * LHS, to avoid having an empty min_lefthand which will confuse later
     * processing. (We don't try to be smart about such cases, just correct.)
     * Likewise for min_righthand.
     */
    if (bms_is_empty(min_lefthand))
        min_lefthand = bms_copy(left_rels);
    if (bms_is_empty(min_righthand))
        min_righthand = bms_copy(right_rels);

    /* Now they'd better be nonempty */
    Assert(!bms_is_empty(min_lefthand));
    Assert(!bms_is_empty(min_righthand));
    /* Shouldn't overlap either */
    Assert(!bms_overlap(min_lefthand, min_righthand));

    sjinfo->min_lefthand = min_lefthand;
    sjinfo->min_righthand = min_righthand;

    return sjinfo;
}


/*****************************************************************************
 *
 *    QUALIFICATIONS
 *
 *****************************************************************************/

/*
 * distribute_qual_to_rels
 *    Add clause information to either the baserestrictinfo or joininfo list
 *    (depending on whether the clause is a join) of each base relation
 *    mentioned in the clause.  A RestrictInfo node is created and added to
 *    the appropriate list for each rel.  Alternatively, if the clause uses a
 *    mergejoinable operator and is not delayed by outer-join rules, enter
 *    the left- and right-side expressions into the query's list of
 *    EquivalenceClasses.
 *
 * 'clause': the qual clause to be distributed
 * 'is_deduced': TRUE if the qual came from implied-equality deduction
 * 'below_outer_join': TRUE if the qual is from a JOIN/ON that is below the
 *      nullable side of a higher-level outer join
 * 'jointype': type of join the qual is from (JOIN_INNER for a WHERE clause)
 * 'qualscope': set of baserels the qual's syntactic scope covers
 * 'ojscope': NULL if not an outer-join qual, else the minimum set of baserels
 *      needed to form this join
 * 'outerjoin_nonnullable': NULL if not an outer-join qual, else the set of
 *      baserels appearing on the outer (nonnullable) side of the join
 *      (for FULL JOIN this includes both sides of the join, and must in fact
 *      equal qualscope)
 * 'deduced_nullable_relids': if is_deduced is TRUE, the nullable relids to
 *      impute to the clause; otherwise NULL
 *
 * 'qualscope' identifies what level of JOIN the qual came from syntactically.
 * 'ojscope' is needed if we decide to force the qual up to the outer-join
 * level, which will be ojscope not necessarily qualscope.
 *
 * In normal use (when is_deduced is FALSE), at the time this is called,
 * root->join_info_list must contain entries for all and only those special
 * joins that are syntactically below this qual.  But when is_deduced is TRUE,
 * we are adding new deduced clauses after completion of deconstruct_jointree,
 * so it cannot be assumed that root->join_info_list has anything to do with
 * qual placement.
 */
static void
distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                        bool is_deduced,
                        bool below_outer_join,
                        JoinType jointype,
                        Relids qualscope,
                        Relids ojscope,
                        Relids outerjoin_nonnullable,
                        Relids deduced_nullable_relids)
{
    Relids      relids;
    bool        is_pushed_down;
    bool        outerjoin_delayed;
    bool        pseudoconstant = false;
    bool        maybe_equivalence;
    bool        maybe_outer_join;
    Relids      nullable_relids;
    RestrictInfo *restrictinfo;

    /*
     * Retrieve all relids mentioned within the clause.
     */
    relids = pull_varnos(clause);

    /*
     * Normally relids is a subset of qualscope, and we like to check that
     * here as a crosscheck on the parser and rewriter.  That need not be the
     * case when there are LATERAL RTEs, however: the clause could contain
     * references to rels outside its syntactic scope as a consequence of
     * pull-up of such references from a LATERAL subquery below it.  So, only
     * check if the query contains no LATERAL RTEs.
     *
     * However, if it's an outer-join clause, we always insist that relids be
     * a subset of ojscope.  This is safe because is_simple_subquery()
     * disallows pullup of LATERAL subqueries that could cause the restriction
     * to be violated.
     */
    if (!root->hasLateralRTEs && !bms_is_subset(relids, qualscope))
        elog(ERROR, "JOIN qualification cannot refer to other relations");
    if (ojscope && !bms_is_subset(relids, ojscope))
        elog(ERROR, "JOIN qualification cannot refer to other relations");

    /*
     * If the clause is variable-free, our normal heuristic for pushing it
     * down to just the mentioned rels doesn't work, because there are none.
     *
     * If the clause is an outer-join clause, we must force it to the OJ's
     * semantic level to preserve semantics.
     *
     * Otherwise, when the clause contains volatile functions, we force it to
     * be evaluated at its original syntactic level.  This preserves the
     * expected semantics.
     *
     * When the clause contains no volatile functions either, it is actually a
     * pseudoconstant clause that will not change value during any one
     * execution of the plan, and hence can be used as a one-time qual in a
     * gating Result plan node.  We put such a clause into the regular
     * RestrictInfo lists for the moment, but eventually createplan.c will
     * pull it out and make a gating Result node immediately above whatever
     * plan node the pseudoconstant clause is assigned to.  It's usually best
     * to put a gating node as high in the plan tree as possible. If we are
     * not below an outer join, we can actually push the pseudoconstant qual
     * all the way to the top of the tree.  If we are below an outer join, we
     * leave the qual at its original syntactic level (we could push it up to
     * just below the outer join, but that seems more complex than it's
     * worth).
     */
    if (bms_is_empty(relids))
    {
        if (ojscope)
        {
            /* clause is attached to outer join, eval it there */
            relids = bms_copy(ojscope);
            /* mustn't use as gating qual, so don't mark pseudoconstant */
        }
        else
        {
            /* eval at original syntactic level */
            relids = bms_copy(qualscope);
            if (!contain_volatile_functions(clause))
            {
                /* mark as gating qual */
                pseudoconstant = true;
                /* tell createplan.c to check for gating quals */
                root->hasPseudoConstantQuals = true;
                /* if not below outer join, push it to top of tree */
                if (!below_outer_join)
                {
                    relids =
                        get_relids_in_jointree((Node *) root->parse->jointree,
                                               false);
                    qualscope = bms_copy(relids);
                }
            }
        }
    }

    /*----------
     * Check to see if clause application must be delayed by outer-join
     * considerations.
     *
     * A word about is_pushed_down: we mark the qual as "pushed down" if
     * it is (potentially) applicable at a level different from its original
     * syntactic level.  This flag is used to distinguish OUTER JOIN ON quals
     * from other quals pushed down to the same joinrel.  The rules are:
     *      WHERE quals and INNER JOIN quals: is_pushed_down = true.
     *      Non-degenerate OUTER JOIN quals: is_pushed_down = false.
     *      Degenerate OUTER JOIN quals: is_pushed_down = true.
     * A "degenerate" OUTER JOIN qual is one that doesn't mention the
     * non-nullable side, and hence can be pushed down into the nullable side
     * without changing the join result.  It is correct to treat it as a
     * regular filter condition at the level where it is evaluated.
     *
     * Note: it is not immediately obvious that a simple boolean is enough
     * for this: if for some reason we were to attach a degenerate qual to
     * its original join level, it would need to be treated as an outer join
     * qual there.  However, this cannot happen, because all the rels the
     * clause mentions must be in the outer join's min_righthand, therefore
     * the join it needs must be formed before the outer join; and we always
     * attach quals to the lowest level where they can be evaluated.  But
     * if we were ever to re-introduce a mechanism for delaying evaluation
     * of "expensive" quals, this area would need work.
     *----------
     */
    if (is_deduced)
    {
        /*
         * If the qual came from implied-equality deduction, it should not be
         * outerjoin-delayed, else deducer blew it.  But we can't check this
         * because the join_info_list may now contain OJs above where the qual
         * belongs.  For the same reason, we must rely on caller to supply the
         * correct nullable_relids set.
         */
        Assert(!ojscope);
        is_pushed_down = true;
        outerjoin_delayed = false;
        nullable_relids = deduced_nullable_relids;
        /* Don't feed it back for more deductions */
        maybe_equivalence = false;
        maybe_outer_join = false;
    }
    else if (bms_overlap(relids, outerjoin_nonnullable))
    {
        /*
         * The qual is attached to an outer join and mentions (some of the)
         * rels on the nonnullable side, so it's not degenerate.
         *
         * We can't use such a clause to deduce equivalence (the left and
         * right sides might be unequal above the join because one of them has
         * gone to NULL) ... but we might be able to use it for more limited
         * deductions, if it is mergejoinable.  So consider adding it to the
         * lists of set-aside outer-join clauses.
         */
        is_pushed_down = false;
        maybe_equivalence = false;
        maybe_outer_join = true;

        /* Check to see if must be delayed by lower outer join */
        outerjoin_delayed = check_outerjoin_delay(root,
                                                  &relids,
                                                  &nullable_relids,
                                                  false);

        /*
         * Now force the qual to be evaluated exactly at the level of joining
         * corresponding to the outer join.  We cannot let it get pushed down
         * into the nonnullable side, since then we'd produce no output rows,
         * rather than the intended single null-extended row, for any
         * nonnullable-side rows failing the qual.
         *
         * (Do this step after calling check_outerjoin_delay, because that
         * trashes relids.)
         */
        Assert(ojscope);
        relids = ojscope;
        Assert(!pseudoconstant);
    }
    else
    {
        /*
         * Normal qual clause or degenerate outer-join clause.  Either way, we
         * can mark it as pushed-down.
         */
        is_pushed_down = true;

        /* Check to see if must be delayed by lower outer join */
        outerjoin_delayed = check_outerjoin_delay(root,
                                                  &relids,
                                                  &nullable_relids,
                                                  true);

        if (outerjoin_delayed)
        {
            /* Should still be a subset of current scope ... */
            Assert(root->hasLateralRTEs || bms_is_subset(relids, qualscope));
            Assert(ojscope == NULL || bms_is_subset(relids, ojscope));

            /*
             * Because application of the qual will be delayed by outer join,
             * we mustn't assume its vars are equal everywhere.
             */
            maybe_equivalence = false;

            /*
             * It's possible that this is an IS NULL clause that's redundant
             * with a lower antijoin; if so we can just discard it.  We need
             * not test in any of the other cases, because this will only be
             * possible for pushed-down, delayed clauses.
             */
            if (check_redundant_nullability_qual(root, clause))
                return;
        }
        else
        {
            /*
             * Qual is not delayed by any lower outer-join restriction, so we
             * can consider feeding it to the equivalence machinery. However,
             * if it's itself within an outer-join clause, treat it as though
             * it appeared below that outer join (note that we can only get
             * here when the clause references only nullable-side rels).
             */
            maybe_equivalence = true;
            if (outerjoin_nonnullable != NULL)
                below_outer_join = true;
        }

        /*
         * Since it doesn't mention the LHS, it's certainly not useful as a
         * set-aside OJ clause, even if it's in an OJ.
         */
        maybe_outer_join = false;
    }

    /*
     * Build the RestrictInfo node itself.
     */
    restrictinfo = make_restrictinfo((Expr *) clause,
                                     is_pushed_down,
                                     outerjoin_delayed,
                                     pseudoconstant,
                                     relids,
                                     outerjoin_nonnullable,
                                     nullable_relids);

    /*
     * If it's a join clause (either naturally, or because delayed by
     * outer-join rules), add vars used in the clause to targetlists of their
     * relations, so that they will be emitted by the plan nodes that scan
     * those relations (else they won't be available at the join node!).
     *
     * Note: if the clause gets absorbed into an EquivalenceClass then this
     * may be unnecessary, but for now we have to do it to cover the case
     * where the EC becomes ec_broken and we end up reinserting the original
     * clauses into the plan.
     */
    if (bms_membership(relids) == BMS_MULTIPLE)
    {
        List       *vars = pull_var_clause(clause,
                                           PVC_RECURSE_AGGREGATES,
                                           PVC_INCLUDE_PLACEHOLDERS);

        add_vars_to_targetlist(root, vars, relids, false);
        list_free(vars);
    }

    /*
     * We check "mergejoinability" of every clause, not only join clauses,
     * because we want to know about equivalences between vars of the same
     * relation, or between vars and consts.
     */
    check_mergejoinable(restrictinfo);

    /*
     * If it is a true equivalence clause, send it to the EquivalenceClass
     * machinery.  We do *not* attach it directly to any restriction or join
     * lists.  The EC code will propagate it to the appropriate places later.
     *
     * If the clause has a mergejoinable operator and is not
     * outerjoin-delayed, yet isn't an equivalence because it is an outer-join
     * clause, the EC code may yet be able to do something with it.  We add it
     * to appropriate lists for further consideration later.  Specifically:
     *
     * If it is a left or right outer-join qualification that relates the two
     * sides of the outer join (no funny business like leftvar1 = leftvar2 +
     * rightvar), we add it to root->left_join_clauses or
     * root->right_join_clauses according to which side the nonnullable
     * variable appears on.
     *
     * If it is a full outer-join qualification, we add it to
     * root->full_join_clauses.  (Ideally we'd discard cases that aren't
     * leftvar = rightvar, as we do for left/right joins, but this routine
     * doesn't have the info needed to do that; and the current usage of the
     * full_join_clauses list doesn't require that, so it's not currently
     * worth complicating this routine's API to make it possible.)
     *
     * If none of the above hold, pass it off to
     * distribute_restrictinfo_to_rels().
     *
     * In all cases, it's important to initialize the left_ec and right_ec
     * fields of a mergejoinable clause, so that all possibly mergejoinable
     * expressions have representations in EquivalenceClasses.  If
     * process_equivalence is successful, it will take care of that;
     * otherwise, we have to call initialize_mergeclause_eclasses to do it.
     */
    if (restrictinfo->mergeopfamilies)
    {
        if (maybe_equivalence)
        {
            if (check_equivalence_delay(root, restrictinfo) &&
                process_equivalence(root, restrictinfo, below_outer_join))
                return;
            /* EC rejected it, so set left_ec/right_ec the hard way ... */
            initialize_mergeclause_eclasses(root, restrictinfo);
            /* ... and fall through to distribute_restrictinfo_to_rels */
        }
        else if (maybe_outer_join && restrictinfo->can_join)
        {
            /* we need to set up left_ec/right_ec the hard way */
            initialize_mergeclause_eclasses(root, restrictinfo);
            /* now see if it should go to any outer-join lists */
            if (bms_is_subset(restrictinfo->left_relids,
                              outerjoin_nonnullable) &&
                !bms_overlap(restrictinfo->right_relids,
                             outerjoin_nonnullable))
            {
                /* we have outervar = innervar */
                root->left_join_clauses = lappend(root->left_join_clauses,
                                                  restrictinfo);
                return;
            }
            if (bms_is_subset(restrictinfo->right_relids,
                              outerjoin_nonnullable) &&
                !bms_overlap(restrictinfo->left_relids,
                             outerjoin_nonnullable))
            {
                /* we have innervar = outervar */
                root->right_join_clauses = lappend(root->right_join_clauses,
                                                   restrictinfo);
                return;
            }
            if (jointype == JOIN_FULL)
            {
                /* FULL JOIN (above tests cannot match in this case) */
                root->full_join_clauses = lappend(root->full_join_clauses,
                                                  restrictinfo);
                return;
            }
            /* nope, so fall through to distribute_restrictinfo_to_rels */
        }
        else
        {
            /* we still need to set up left_ec/right_ec */
            initialize_mergeclause_eclasses(root, restrictinfo);
        }
    }

    /* No EC special case applies, so push it into the clause lists */
    distribute_restrictinfo_to_rels(root, restrictinfo);
}

/*
 * check_outerjoin_delay
 *      Detect whether a qual referencing the given relids must be delayed
 *      in application due to the presence of a lower outer join, and/or
 *      may force extra delay of higher-level outer joins.
 *
 * If the qual must be delayed, add relids to *relids_p to reflect the lowest
 * safe level for evaluating the qual, and return TRUE.  Any extra delay for
 * higher-level joins is reflected by setting delay_upper_joins to TRUE in
 * SpecialJoinInfo structs.  We also compute nullable_relids, the set of
 * referenced relids that are nullable by lower outer joins (note that this
 * can be nonempty even for a non-delayed qual).
 *
 * For an is_pushed_down qual, we can evaluate the qual as soon as (1) we have
 * all the rels it mentions, and (2) we are at or above any outer joins that
 * can null any of these rels and are below the syntactic location of the
 * given qual.  We must enforce (2) because pushing down such a clause below
 * the OJ might cause the OJ to emit null-extended rows that should not have
 * been formed, or that should have been rejected by the clause.  (This is
 * only an issue for non-strict quals, since if we can prove a qual mentioning
 * only nullable rels is strict, we'd have reduced the outer join to an inner
 * join in reduce_outer_joins().)
 *
 * To enforce (2), scan the join_info_list and merge the required-relid sets of
 * any such OJs into the clause's own reference list.  At the time we are
 * called, the join_info_list contains only outer joins below this qual.  We
 * have to repeat the scan until no new relids get added; this ensures that
 * the qual is suitably delayed regardless of the order in which OJs get
 * executed.  As an example, if we have one OJ with LHS=A, RHS=B, and one with
 * LHS=B, RHS=C, it is implied that these can be done in either order; if the
 * B/C join is done first then the join to A can null C, so a qual actually
 * mentioning only C cannot be applied below the join to A.
 *
 * For a non-pushed-down qual, this isn't going to determine where we place the
 * qual, but we need to determine outerjoin_delayed and nullable_relids anyway
 * for use later in the planning process.
 *
 * Lastly, a pushed-down qual that references the nullable side of any current
 * join_info_list member and has to be evaluated above that OJ (because its
 * required relids overlap the LHS too) causes that OJ's delay_upper_joins
 * flag to be set TRUE.  This will prevent any higher-level OJs from
 * being interchanged with that OJ, which would result in not having any
 * correct place to evaluate the qual.  (The case we care about here is a
 * sub-select WHERE clause within the RHS of some outer join.  The WHERE
 * clause must effectively be treated as a degenerate clause of that outer
 * join's condition.  Rather than trying to match such clauses with joins
 * directly, we set delay_upper_joins here, and when the upper outer join
 * is processed by make_outerjoininfo, it will refrain from allowing the
 * two OJs to commute.)
 */
static bool
check_outerjoin_delay(PlannerInfo *root,
                      Relids *relids_p, /* in/out parameter */
                      Relids *nullable_relids_p,        /* output parameter */
                      bool is_pushed_down)
{
    Relids      relids;
    Relids      nullable_relids;
    bool        outerjoin_delayed;
    bool        found_some;

    /* fast path if no special joins */
    if (root->join_info_list == NIL)
    {
        *nullable_relids_p = NULL;
        return false;
    }

    /* must copy relids because we need the original value at the end */
    relids = bms_copy(*relids_p);
    nullable_relids = NULL;
    outerjoin_delayed = false;
    do
    {
        ListCell   *l;

        found_some = false;
        foreach(l, root->join_info_list)
        {
            SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);

            /* do we reference any nullable rels of this OJ? */
            if (bms_overlap(relids, sjinfo->min_righthand) ||
                (sjinfo->jointype == JOIN_FULL &&
                 bms_overlap(relids, sjinfo->min_lefthand)))
            {
                /* yes; have we included all its rels in relids? */
                if (!bms_is_subset(sjinfo->min_lefthand, relids) ||
                    !bms_is_subset(sjinfo->min_righthand, relids))
                {
                    /* no, so add them in */
                    relids = bms_add_members(relids, sjinfo->min_lefthand);
                    relids = bms_add_members(relids, sjinfo->min_righthand);
                    outerjoin_delayed = true;
                    /* we'll need another iteration */
                    found_some = true;
                }
                /* track all the nullable rels of relevant OJs */
                nullable_relids = bms_add_members(nullable_relids,
                                                  sjinfo->min_righthand);
                if (sjinfo->jointype == JOIN_FULL)
                    nullable_relids = bms_add_members(nullable_relids,
                                                      sjinfo->min_lefthand);
                /* set delay_upper_joins if needed */
                if (is_pushed_down && sjinfo->jointype != JOIN_FULL &&
                    bms_overlap(relids, sjinfo->min_lefthand))
                    sjinfo->delay_upper_joins = true;
            }
        }
    } while (found_some);

    /* identify just the actually-referenced nullable rels */
    nullable_relids = bms_int_members(nullable_relids, *relids_p);

    /* replace *relids_p, and return nullable_relids */
    bms_free(*relids_p);
    *relids_p = relids;
    *nullable_relids_p = nullable_relids;
    return outerjoin_delayed;
}

/*
 * check_equivalence_delay
 *      Detect whether a potential equivalence clause is rendered unsafe
 *      by outer-join-delay considerations.  Return TRUE if it's safe.
 *
 * The initial tests in distribute_qual_to_rels will consider a mergejoinable
 * clause to be a potential equivalence clause if it is not outerjoin_delayed.
 * But since the point of equivalence processing is that we will recombine the
 * two sides of the clause with others, we have to check that each side
 * satisfies the not-outerjoin_delayed condition on its own; otherwise it might
 * not be safe to evaluate everywhere we could place a derived equivalence
 * condition.
 */
static bool
check_equivalence_delay(PlannerInfo *root,
                        RestrictInfo *restrictinfo)
{
    Relids      relids;
    Relids      nullable_relids;

    /* fast path if no special joins */
    if (root->join_info_list == NIL)
        return true;

    /* must copy restrictinfo's relids to avoid changing it */
    relids = bms_copy(restrictinfo->left_relids);
    /* check left side does not need delay */
    if (check_outerjoin_delay(root, &relids, &nullable_relids, true))
        return false;

    /* and similarly for the right side */
    relids = bms_copy(restrictinfo->right_relids);
    if (check_outerjoin_delay(root, &relids, &nullable_relids, true))
        return false;

    return true;
}

/*
 * check_redundant_nullability_qual
 *    Check to see if the qual is an IS NULL qual that is redundant with
 *    a lower JOIN_ANTI join.
 *
 * We want to suppress redundant IS NULL quals, not so much to save cycles
 * as to avoid generating bogus selectivity estimates for them.  So if
 * redundancy is detected here, distribute_qual_to_rels() just throws away
 * the qual.
 */
static bool
check_redundant_nullability_qual(PlannerInfo *root, Node *clause)
{
    Var        *forced_null_var;
    Index       forced_null_rel;
    ListCell   *lc;

    /* Check for IS NULL, and identify the Var forced to NULL */
    forced_null_var = find_forced_null_var(clause);
    if (forced_null_var == NULL)
        return false;
    forced_null_rel = forced_null_var->varno;

    /*
     * If the Var comes from the nullable side of a lower antijoin, the IS
     * NULL condition is necessarily true.
     */
    foreach(lc, root->join_info_list)
    {
        SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);

        if (sjinfo->jointype == JOIN_ANTI &&
            bms_is_member(forced_null_rel, sjinfo->syn_righthand))
            return true;
    }

    return false;
}

/*
 * distribute_restrictinfo_to_rels
 *    Push a completed RestrictInfo into the proper restriction or join
 *    clause list(s).
 *
 * This is the last step of distribute_qual_to_rels() for ordinary qual
 * clauses.  Clauses that are interesting for equivalence-class processing
 * are diverted to the EC machinery, but may ultimately get fed back here.
 */
void
distribute_restrictinfo_to_rels(PlannerInfo *root,
                                RestrictInfo *restrictinfo)
{
    Relids      relids = restrictinfo->required_relids;
    RelOptInfo *rel;

    switch (bms_membership(relids))
    {
        case BMS_SINGLETON:

            /*
             * There is only one relation participating in the clause, so it
             * is a restriction clause for that relation.
             */
            rel = find_base_rel(root, bms_singleton_member(relids));

            /* Add clause to rel's restriction list */
            rel->baserestrictinfo = lappend(rel->baserestrictinfo,
                                            restrictinfo);
            break;
        case BMS_MULTIPLE:

            /*
             * The clause is a join clause, since there is more than one rel
             * in its relid set.
             */

            /*
             * Check for hashjoinable operators.  (We don't bother setting the
             * hashjoin info except in true join clauses.)
             */
            check_hashjoinable(restrictinfo);

            /*
             * Add clause to the join lists of all the relevant relations.
             */
            add_join_clause_to_rels(root, restrictinfo, relids);
            break;
        default:

            /*
             * clause references no rels, and therefore we have no place to
             * attach it.  Shouldn't get here if callers are working properly.
             */
            elog(ERROR, "cannot cope with variable-free clause");
            break;
    }
}

/*
 * process_implied_equality
 *    Create a restrictinfo item that says "item1 op item2", and push it
 *    into the appropriate lists.  (In practice opno is always a btree
 *    equality operator.)
 *
 * "qualscope" is the nominal syntactic level to impute to the restrictinfo.
 * This must contain at least all the rels used in the expressions, but it
 * is used only to set the qual application level when both exprs are
 * variable-free.  Otherwise the qual is applied at the lowest join level
 * that provides all its variables.
 *
 * "nullable_relids" is the set of relids used in the expressions that are
 * potentially nullable below the expressions.  (This has to be supplied by
 * caller because this function is used after deconstruct_jointree, so we
 * don't have knowledge of where the clause items came from.)
 *
 * "both_const" indicates whether both items are known pseudo-constant;
 * in this case it is worth applying eval_const_expressions() in case we
 * can produce constant TRUE or constant FALSE.  (Otherwise it's not,
 * because the expressions went through eval_const_expressions already.)
 *
 * Note: this function will copy item1 and item2, but it is caller's
 * responsibility to make sure that the Relids parameters are fresh copies
 * not shared with other uses.
 *
 * This is currently used only when an EquivalenceClass is found to
 * contain pseudoconstants.  See path/pathkeys.c for more details.
 */
void
process_implied_equality(PlannerInfo *root,
                         Oid opno,
                         Oid collation,
                         Expr *item1,
                         Expr *item2,
                         Relids qualscope,
                         Relids nullable_relids,
                         bool below_outer_join,
                         bool both_const)
{
    Expr       *clause;

    /*
     * Build the new clause.  Copy to ensure it shares no substructure with
     * original (this is necessary in case there are subselects in there...)
     */
    clause = make_opclause(opno,
                           BOOLOID,     /* opresulttype */
                           false,       /* opretset */
                           (Expr *) copyObject(item1),
                           (Expr *) copyObject(item2),
                           InvalidOid,
                           collation);

    /* If both constant, try to reduce to a boolean constant. */
    if (both_const)
    {
        clause = (Expr *) eval_const_expressions(root, (Node *) clause);

        /* If we produced const TRUE, just drop the clause */
        if (clause && IsA(clause, Const))
        {
            Const      *cclause = (Const *) clause;

            Assert(cclause->consttype == BOOLOID);
            if (!cclause->constisnull && DatumGetBool(cclause->constvalue))
                return;
        }
    }

    /*
     * Push the new clause into all the appropriate restrictinfo lists.
     */
    distribute_qual_to_rels(root, (Node *) clause,
                            true, below_outer_join, JOIN_INNER,
                            qualscope, NULL, NULL, nullable_relids);
}

/*
 * build_implied_join_equality --- build a RestrictInfo for a derived equality
 *
 * This overlaps the functionality of process_implied_equality(), but we
 * must return the RestrictInfo, not push it into the joininfo tree.
 *
 * Note: this function will copy item1 and item2, but it is caller's
 * responsibility to make sure that the Relids parameters are fresh copies
 * not shared with other uses.
 *
 * Note: we do not do initialize_mergeclause_eclasses() here.  It is
 * caller's responsibility that left_ec/right_ec be set as necessary.
 */
RestrictInfo *
build_implied_join_equality(Oid opno,
                            Oid collation,
                            Expr *item1,
                            Expr *item2,
                            Relids qualscope,
                            Relids nullable_relids)
{
    RestrictInfo *restrictinfo;
    Expr       *clause;

    /*
     * Build the new clause.  Copy to ensure it shares no substructure with
     * original (this is necessary in case there are subselects in there...)
     */
    clause = make_opclause(opno,
                           BOOLOID,     /* opresulttype */
                           false,       /* opretset */
                           (Expr *) copyObject(item1),
                           (Expr *) copyObject(item2),
                           InvalidOid,
                           collation);

    /*
     * Build the RestrictInfo node itself.
     */
    restrictinfo = make_restrictinfo(clause,
                                     true,      /* is_pushed_down */
                                     false,     /* outerjoin_delayed */
                                     false,     /* pseudoconstant */
                                     qualscope, /* required_relids */
                                     NULL,      /* outer_relids */
                                     nullable_relids);  /* nullable_relids */

    /* Set mergejoinability/hashjoinability flags */
    check_mergejoinable(restrictinfo);
    check_hashjoinable(restrictinfo);

    return restrictinfo;
}


/*****************************************************************************
 *
 *   CHECKS FOR MERGEJOINABLE AND HASHJOINABLE CLAUSES
 *
 *****************************************************************************/

/*
 * check_mergejoinable
 *    If the restrictinfo's clause is mergejoinable, set the mergejoin
 *    info fields in the restrictinfo.
 *
 *    Currently, we support mergejoin for binary opclauses where
 *    the operator is a mergejoinable operator.  The arguments can be
 *    anything --- as long as there are no volatile functions in them.
 */
static void
check_mergejoinable(RestrictInfo *restrictinfo)
{
    Expr       *clause = restrictinfo->clause;
    Oid         opno;
    Node       *leftarg;

    if (restrictinfo->pseudoconstant)
        return;
    if (!is_opclause(clause))
        return;
    if (list_length(((OpExpr *) clause)->args) != 2)
        return;

    opno = ((OpExpr *) clause)->opno;
    leftarg = linitial(((OpExpr *) clause)->args);

    if (op_mergejoinable(opno, exprType(leftarg)) &&
        !contain_volatile_functions((Node *) clause))
        restrictinfo->mergeopfamilies = get_mergejoin_opfamilies(opno);

    /*
     * Note: op_mergejoinable is just a hint; if we fail to find the operator
     * in any btree opfamilies, mergeopfamilies remains NIL and so the clause
     * is not treated as mergejoinable.
     */
}

/*
 * check_hashjoinable
 *    If the restrictinfo's clause is hashjoinable, set the hashjoin
 *    info fields in the restrictinfo.
 *
 *    Currently, we support hashjoin for binary opclauses where
 *    the operator is a hashjoinable operator.  The arguments can be
 *    anything --- as long as there are no volatile functions in them.
 */
static void
check_hashjoinable(RestrictInfo *restrictinfo)
{
    Expr       *clause = restrictinfo->clause;
    Oid         opno;
    Node       *leftarg;

    if (restrictinfo->pseudoconstant)
        return;
    if (!is_opclause(clause))
        return;
    if (list_length(((OpExpr *) clause)->args) != 2)
        return;

    opno = ((OpExpr *) clause)->opno;
    leftarg = linitial(((OpExpr *) clause)->args);

    if (op_hashjoinable(opno, exprType(leftarg)) &&
        !contain_volatile_functions((Node *) clause))
        restrictinfo->hashjoinoperator = opno;
}