Revise collation derivation method and expression-tree representation.

[postgresql] / src / backend / optimizer / plan / initsplan.c

/*-------------------------------------------------------------------------
 *
 * initsplan.c
 *        Target list, qualification, joininfo initialization routines
 *
 * Portions Copyright (c) 1996-2011, 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_operator.h"
#include "catalog/pg_type.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/joininfo.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/placeholder.h"
#include "optimizer/planmain.h"
#include "optimizer/prep.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/var.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


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


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);
static bool check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
                                          Relids *nullable_relids_p, bool is_pushed_down);
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_INCLUDE_PLACEHOLDERS);

        if (tlist_vars != NIL)
        {
                add_vars_to_targetlist(root, tlist_vars, bms_make_singleton(0));
                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.
 */
void
add_vars_to_targetlist(PlannerInfo *root, List *vars, Relids where_needed)
{
        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);

                        phinfo->ph_needed = bms_add_members(phinfo->ph_needed,
                                                                                                where_needed);
                        /*
                         * Update ph_may_need too.  This is currently only necessary
                         * when being called from build_base_rel_tlists, but we may as
                         * well do it always.
                         */
                        phinfo->ph_may_need = bms_add_members(phinfo->ph_may_need,
                                                                                                  where_needed);
                }
                else
                        elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node));
        }
}


/*****************************************************************************
 *
 *        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);
                }
        }
        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);
                }

                /* 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 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 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("SELECT FOR UPDATE/SHARE 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)
 *
 * '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.
 *
 * 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.
 */
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          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);

        /*
         * Cross-check: clause should contain no relids not within its scope.
         * Otherwise the parser messed up.
         */
        if (!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.
                 */
                Assert(!ojscope);
                is_pushed_down = true;
                outerjoin_delayed = false;
                nullable_relids = NULL;
                /* 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(bms_is_subset(relids, qualscope));

                        /*
                         * 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,
                                                                         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_INCLUDE_PLACEHOLDERS);

                add_vars_to_targetlist(root, vars, relids);
                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 (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_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.
 *
 * "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.)
 *
 * 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,
                                                 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;
                }
        }

        /* Make a copy of qualscope to avoid problems if source EC changes */
        qualscope = bms_copy(qualscope);

        /*
         * 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);
}

/*
 * 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: 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)
{
        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);

        /* Make a copy of qualscope to avoid problems if source EC changes */
        qualscope = bms_copy(qualscope);

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