initsplan.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

		/*
		 * Since we do this bottom-up, any outer-rels previously marked should
		 * be within the new outer join set.
		 */
		Assert(bms_is_subset(rel->outerjoinset, outerrels));

		/*
		 * 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 target rel is FOR UPDATE/SHARE. 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 (list_member_int(root->parse->rowMarks, relno))
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("SELECT FOR UPDATE/SHARE 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 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.  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
 * 'is_pushed_down': if TRUE, force the clause to be marked 'is_pushed_down'
 *		(this indicates the clause came from a FromExpr, not a JoinExpr)
 * '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.
 * '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
 * 'is_pushed_down' will be TRUE.
 */
static void
distribute_qual_to_rels(PlannerInfo *root, Node *clause,
						bool is_pushed_down,
						bool is_deduced,
						bool below_outer_join,
						Relids outerjoin_nonnullable,
						Relids qualscope)
{
	Relids		relids;
	bool		outerjoin_delayed;
	bool		maybe_equijoin;
	bool		maybe_outer_join;
	RestrictInfo *restrictinfo;
	RelOptInfo *rel;
	List	   *vars;

	/*
	 * 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 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 (is_deduced)
	{
		/*
		 * If the qual came from implied-equality deduction, we always
		 * evaluate the qual at its natural semantic level.  It is the
		 * responsibility of the deducer not to create any quals that should
		 * be delayed by outer-join rules.
		 */
		Assert(bms_equal(relids, qualscope));
		/* Needn't feed it back for more deductions */
		outerjoin_delayed = false;
		maybe_equijoin = 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.  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,
		 * except for not setting maybe_equijoin (see below).
		 */
		relids = qualscope;
		outerjoin_delayed = true;

		/*
		 * We can't use such a clause to deduce equijoin (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
		 * purposes.  Note: for the current uses of deductions from an
		 * outer-join clause, it seems safe to make the deductions even when
		 * the clause is below a higher-level outer join; so we do not check
		 * below_outer_join here.
		 */
		maybe_equijoin = false;
		maybe_outer_join = true;
	}
	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;

		outerjoin_delayed = false;
		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);
				outerjoin_delayed = true;
			}
		}
		bms_free(tmprelids);

		if (bms_is_subset(addrelids, relids))
		{
			/*
			 * Qual is not delayed by any lower outer-join restriction. If it
			 * is not itself below or within an outer join, we can consider it
			 * "valid everywhere", so consider feeding it to the equijoin
			 * machinery.  (If it is within an outer join, we can't consider
			 * it "valid everywhere": once the contained variables have gone
			 * to NULL, we'd be asserting things like NULL = NULL, which is
			 * not true.)
			 */
			if (!below_outer_join && outerjoin_nonnullable == NULL)
				maybe_equijoin = true;
			else
				maybe_equijoin = false;
		}
		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.
			 */
			maybe_equijoin = false;
		}
		bms_free(addrelids);
		maybe_outer_join = false;
	}

	/*
	 * 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".
	 */
	if (!is_pushed_down)
		is_pushed_down = !bms_equal(relids, qualscope);

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

	/*
	 * Figure out where to attach it.
	 */
	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.
			 */
			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 (!is_deduced ||
				!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.
			 */

			/*
			 * 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!).
			 */
			vars = pull_var_clause(clause, false);
			add_vars_to_targetlist(root, vars, relids);
			list_free(vars);
			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, we may be able to deduce
	 * more things from it under the principle of transitivity.
	 *
	 * If it 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).  Pass such clauses
	 * to add_equijoined_keys.
	 *
	 * 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 (restrictinfo->mergejoinoperator != InvalidOid)
	{
		if (maybe_equijoin)
			add_equijoined_keys(root, restrictinfo);
		else if (maybe_outer_join && restrictinfo->can_join)
		{
			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);
			}
			else 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);
			}