initsplan.c

来自「PostgreSQL7.4.6 for Linux」· C语言 代码 · 共 974 行 · 第 1/3 页

		 * Presently the executor cannot support FOR UPDATE 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 target rel is FOR UPDATE.
		 * It's sufficient to make this check once per rel, so do it only
		 * if rel wasn't already known nullable.
		 */
		if (rel->outerjoinset == NULL)
		{
			if (intMember(relno, root->rowMarks))
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("SELECT FOR UPDATE cannot be applied to the nullable side of an outer join")));
		}

		rel->outerjoinset = outerrels;
	}
	bms_free(tmprelids);
}

/*
 * distribute_qual_to_rels
 *	  Add clause information to either the 'RestrictInfo' or 'JoinInfo' field
 *	  (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.  Also, 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 lists of
 *	  equijoined vars.
 *
 * 'clause': the qual clause to be distributed
 * 'ispusheddown': if TRUE, force the clause to be marked 'ispusheddown'
 *		(this indicates the clause came from a FromExpr, not a JoinExpr)
 * 'isdeduced': TRUE if the qual came from implied-equality deduction
 * 'outerjoin_nonnullable': NULL if not an outer-join qual, else the set of
 *		baserels appearing on the outer (nonnullable) side of the join
 * 'qualscope': set of baserels the qual's syntactic scope covers
 *
 * 'qualscope' identifies what level of JOIN the qual came from.  For a top
 * level qual (WHERE qual), qualscope lists all baserel ids and in addition
 * 'ispusheddown' will be TRUE.
 */
static void
distribute_qual_to_rels(Query *root, Node *clause,
						bool ispusheddown,
						bool isdeduced,
						Relids outerjoin_nonnullable,
						Relids qualscope)
{
	RestrictInfo *restrictinfo = makeNode(RestrictInfo);
	RelOptInfo *rel;
	Relids		relids;
	List	   *vars;
	bool		can_be_equijoin;

	restrictinfo->clause = (Expr *) clause;
	restrictinfo->subclauseindices = NIL;
	restrictinfo->eval_cost.startup = -1;		/* not computed until
												 * needed */
	restrictinfo->this_selec = -1;		/* not computed until needed */
	restrictinfo->left_relids = NULL;	/* set below, if join clause */
	restrictinfo->right_relids = NULL;
	restrictinfo->mergejoinoperator = InvalidOid;
	restrictinfo->left_sortop = InvalidOid;
	restrictinfo->right_sortop = InvalidOid;
	restrictinfo->left_pathkey = NIL;	/* not computable yet */
	restrictinfo->right_pathkey = NIL;
	restrictinfo->left_mergescansel = -1;		/* not computed until
												 * needed */
	restrictinfo->right_mergescansel = -1;
	restrictinfo->hashjoinoperator = InvalidOid;
	restrictinfo->left_bucketsize = -1; /* not computed until needed */
	restrictinfo->right_bucketsize = -1;

	/*
	 * Retrieve all relids and vars contained within the clause.
	 */
	clause_get_relids_vars(clause, &relids, &vars);

	/*
	 * 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 may not refer to other relations");

	/*
	 * If the clause is variable-free, we force it to be evaluated at its
	 * original syntactic level.  Note that this should not happen for
	 * top-level clauses, because query_planner() special-cases them.  But
	 * it will happen for variable-free JOIN/ON clauses.  We don't have to
	 * be real smart about such a case, we just have to be correct.
	 */
	if (bms_is_empty(relids))
		relids = qualscope;

	/*
	 * Check to see if clause application must be delayed by outer-join
	 * considerations.
	 */
	if (isdeduced)
	{
		/*
		 * If the qual came from implied-equality deduction, we can
		 * evaluate the qual at its natural semantic level.  It is not
		 * affected by any outer-join rules (else we'd not have decided
		 * the vars were equal).
		 */
		Assert(bms_equal(relids, qualscope));
		can_be_equijoin = true;
	}
	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.  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.
		 *
		 * Note: an outer-join qual that mentions only nullable-side rels can
		 * be pushed down into the nullable side without changing the join
		 * result, so we treat it the same as an ordinary inner-join qual.
		 */
		relids = qualscope;
		can_be_equijoin = false;
	}
	else
	{
		/*
		 * For a non-outer-join 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. To enforce the
		 * latter, scan the base rels listed in relids, and merge their
		 * outer-join sets into the clause's own reference list.  At the
		 * time we are called, the outerjoinset of each baserel will show
		 * exactly those outer joins that are below the qual in the join
		 * tree.
		 */
		Relids		addrelids = NULL;
		Relids		tmprelids;
		int			relno;

		tmprelids = bms_copy(relids);
		while ((relno = bms_first_member(tmprelids)) >= 0)
		{
			RelOptInfo *rel = find_base_rel(root, relno);

			if (rel->outerjoinset != NULL)
				addrelids = bms_add_members(addrelids, rel->outerjoinset);
		}
		bms_free(tmprelids);

		if (bms_is_subset(addrelids, relids))
		{
			/* Qual is not affected by any outer-join restriction */
			can_be_equijoin = true;
		}
		else
		{
			relids = bms_union(relids, addrelids);
			/* 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.
			 */
			can_be_equijoin = false;
		}
		bms_free(addrelids);
	}

	/*
	 * Mark the qual as "pushed down" if it can be applied at a level
	 * below its original syntactic level.	This allows us to distinguish
	 * original JOIN/ON quals from higher-level quals pushed down to the
	 * same joinrel. A qual originating from WHERE is always considered
	 * "pushed down".
	 */
	restrictinfo->ispusheddown = ispusheddown || !bms_equal(relids,
															qualscope);

	switch (bms_membership(relids))
	{
		case BMS_SINGLETON:

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

			/*
			 * Check for a "mergejoinable" clause even though it's not a
			 * join clause.  This is so that we can recognize that "a.x =
			 * a.y" makes x and y eligible to be considered equal, even
			 * when they belong to the same rel.  Without this, we would
			 * not recognize that "a.x = a.y AND a.x = b.z AND a.y = c.q"
			 * allows us to consider z and q equal after their rels are
			 * joined.
			 */
			if (can_be_equijoin)
				check_mergejoinable(restrictinfo);

			/*
			 * If the clause was deduced from implied equality, check to
			 * see whether it is redundant with restriction clauses we
			 * already have for this rel.  Note we cannot apply this check
			 * to user-written clauses, since we haven't found the
			 * canonical pathkey sets yet while processing user clauses.
			 * (NB: no comparable check is done in the join-clause case;
			 * redundancy will be detected when the join clause is moved
			 * into a join rel's restriction list.)
			 */
			if (!isdeduced ||
			!qual_is_redundant(root, restrictinfo, rel->baserestrictinfo))
			{
				/* Add clause to rel's restriction list */
				rel->baserestrictinfo = lappend(rel->baserestrictinfo,
												restrictinfo);
			}
			break;
		case BMS_MULTIPLE:

			/*
			 * 'clause' is a join clause, since there is more than one rel
			 * in the relid set.   Set additional RestrictInfo fields for
			 * joining.  First, does it look like a normal join clause,
			 * i.e., a binary operator relating expressions that come from
			 * distinct relations?	If so we might be able to use it in a
			 * join algorithm.
			 */
			if (is_opclause(clause) && length(((OpExpr *) clause)->args) == 2)
			{
				Relids		left_relids;
				Relids		right_relids;

				left_relids = pull_varnos(get_leftop((Expr *) clause));
				right_relids = pull_varnos(get_rightop((Expr *) clause));
				if (!bms_is_empty(left_relids) &&
					!bms_is_empty(right_relids) &&
					!bms_overlap(left_relids, right_relids))
				{
					restrictinfo->left_relids = left_relids;
					restrictinfo->right_relids = right_relids;
				}
			}

			/*
			 * Now check for hash or mergejoinable operators.
			 *
			 * We don't bother setting the hashjoin info if we're not going
			 * to need it.	We do want to know about mergejoinable ops in
			 * all cases, however, because we use mergejoinable ops for
			 * other purposes such as detecting redundant clauses.
			 */
			check_mergejoinable(restrictinfo);
			if (enable_hashjoin)
				check_hashjoinable(restrictinfo);

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

			/*
			 * Add vars used in the join 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!).
			 */
			add_vars_to_targetlist(root, vars, 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;
	}

	/*
	 * If the clause has a mergejoinable operator, and is not an
	 * outer-join qualification nor bubbled up due to an outer join, then
	 * the two sides represent equivalent PathKeyItems for path keys: any
	 * path that is sorted by one side will also be sorted by the other
	 * (as soon as the two rels are joined, that is).  Record the key
	 * equivalence for future use.	(We can skip this for a deduced
	 * clause, since the keys are already known equivalent in that case.)
	 */
	if (can_be_equijoin && restrictinfo->mergejoinoperator != InvalidOid &&
		!isdeduced)
		add_equijoined_keys(root, restrictinfo);
}

/*
 * process_implied_equality
 *	  Check to see whether we already have a restrictinfo item that says
 *	  item1 = item2, and create one if not; or if delete_it is true,
 *	  remove any such restrictinfo item.
 *
 * This processing is a consequence of transitivity of mergejoin equality:
 * if we have mergejoinable clauses A = B and B = C, we can deduce A = C
 * (where = is an appropriate mergejoinable operator).	See path/pathkeys.c
 * for more details.
 */
void
process_implied_equality(Query *root,
						 Node *item1, Node *item2,
						 Oid sortop1, Oid sortop2,
						 Relids item1_relids, Relids item2_relids,
						 bool delete_it)
{
	Relids		relids;
	BMS_Membership membership;
	RelOptInfo *rel1;
	List	   *restrictlist;