initsplan.c

来自「postgresql8.3.4源码,开源数据库」· C语言 代码 · 共 1,362 行 · 第 1/4 页

		 */
		foreach(l, (List *) f->quals)
			distribute_qual_to_rels(root, (Node *) lfirst(l),
									false, below_outer_join,
									*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;
		OuterJoinInfo *ojinfo;
		ListCell   *qual;

		/*
		 * 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 an oj_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:
				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_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;
			case JOIN_RIGHT:
				/* notice we switch leftids and rightids */
				leftjoinlist = deconstruct_recurse(root, j->larg,
												   true,
												   &rightids, &right_inners);
				rightjoinlist = deconstruct_recurse(root, j->rarg,
													below_outer_join,
													&leftids, &left_inners);
				*qualscope = bms_union(leftids, rightids);
				*inner_join_rels = bms_union(left_inners, right_inners);
				nonnullable_rels = leftids;
				break;
			default:
				elog(ERROR, "unrecognized join type: %d",
					 (int) j->jointype);
				nonnullable_rels = NULL;		/* keep compiler quiet */
				leftjoinlist = rightjoinlist = NIL;
				break;
		}

		/*
		 * For an OJ, form the OuterJoinInfo now, because we need the OJ's
		 * semantic scope (ojscope) to pass to distribute_qual_to_rels.  But
		 * we mustn't add it to oj_info_list just yet, because we don't want
		 * distribute_qual_to_rels to think it is an outer join below us.
		 */
		if (j->jointype != JOIN_INNER)
		{
			ojinfo = make_outerjoininfo(root,
										leftids, rightids,
										*inner_join_rels,
										(j->jointype == JOIN_FULL),
										j->quals);
			ojscope = bms_union(ojinfo->min_lefthand, ojinfo->min_righthand);
		}
		else
		{
			ojinfo = NULL;
			ojscope = NULL;
		}

		/* Process the qual clauses */
		foreach(qual, (List *) j->quals)
			distribute_qual_to_rels(root, (Node *) lfirst(qual),
									false, below_outer_join,
									*qualscope, ojscope, nonnullable_rels);

		/* Now we can add the OuterJoinInfo to oj_info_list */
		if (ojinfo)
			root->oj_info_list = lappend(root->oj_info_list, ojinfo);

		/*
		 * 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 an OuterJoinInfo 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
 *	is_full_join: what it says
 *	clause: the outer join's join condition
 *
 * If the join is a RIGHT JOIN, left_rels and right_rels are switched by
 * the caller, so that left_rels is always the nonnullable side.  Hence
 * we need only distinguish the LEFT and FULL cases.
 *
 * The node should eventually be appended to root->oj_info_list, but we
 * do not do that here.
 *
 * Note: we assume that this function is invoked bottom-up, so that
 * root->oj_info_list already contains entries for all outer joins that are
 * syntactically below this one.
 */
static OuterJoinInfo *
make_outerjoininfo(PlannerInfo *root,
				   Relids left_rels, Relids right_rels,
				   Relids inner_join_rels,
				   bool is_full_join, Node *clause)
{
	OuterJoinInfo *ojinfo = makeNode(OuterJoinInfo);
	Relids		clause_relids;
	Relids		strict_relids;
	Relids		min_lefthand;
	Relids		min_righthand;
	ListCell   *l;

	/*
	 * 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.
	 */
	foreach(l, root->parse->rowMarks)
	{
		RowMarkClause *rc = (RowMarkClause *) lfirst(l);

		if (bms_is_member(rc->rti, right_rels) ||
			(is_full_join && 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")));
	}

	/* this always starts out false */
	ojinfo->delay_upper_joins = false;

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

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

	/* Remember whether the clause is strict for any LHS relations */
	ojinfo->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->oj_info_list)
	{
		OuterJoinInfo *otherinfo = (OuterJoinInfo *) lfirst(l);

		/* ignore full joins --- other mechanisms preserve their ordering */
		if (otherinfo->is_full_join)
			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.)
		 *
		 * 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) &&
			bms_overlap(clause_relids, otherinfo->syn_righthand) &&
			!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 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) ||
				!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);
			}
		}
	}

	/*
	 * 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));

	ojinfo->min_lefthand = min_lefthand;