prepjointree.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

				break;
			default:
				elog(ERROR, "unrecognized join type: %d",
					 (int) j->jointype);
				break;
		}
	}
	else
		elog(ERROR, "unrecognized node type: %d",
			 (int) nodeTag(jtnode));
	return jtnode;
}

/*
 * is_simple_subquery
 *	  Check a subquery in the range table to see if it's simple enough
 *	  to pull up into the parent query.
 */
static bool
is_simple_subquery(Query *subquery)
{
	/*
	 * Let's just make sure it's a valid subselect ...
	 */
	if (!IsA(subquery, Query) ||
		subquery->commandType != CMD_SELECT ||
		subquery->resultRelation != 0 ||
		subquery->into != NULL)
		elog(ERROR, "subquery is bogus");

	/*
	 * Can't currently pull up a query with setops. Maybe after querytree
	 * redesign...
	 */
	if (subquery->setOperations)
		return false;

	/*
	 * Can't pull up a subquery involving grouping, aggregation, sorting, or
	 * limiting.
	 */
	if (subquery->hasAggs ||
		subquery->groupClause ||
		subquery->havingQual ||
		subquery->sortClause ||
		subquery->distinctClause ||
		subquery->limitOffset ||
		subquery->limitCount)
		return false;

	/*
	 * Don't pull up a subquery that has any set-returning functions in its
	 * targetlist.	Otherwise we might well wind up inserting set-returning
	 * functions into places where they mustn't go, such as quals of higher
	 * queries.
	 */
	if (expression_returns_set((Node *) subquery->targetList))
		return false;

	/*
	 * Hack: don't try to pull up a subquery with an empty jointree.
	 * query_planner() will correctly generate a Result plan for a jointree
	 * that's totally empty, but I don't think the right things happen if an
	 * empty FromExpr appears lower down in a jointree. Not worth working hard
	 * on this, just to collapse SubqueryScan/Result into Result...
	 */
	if (subquery->jointree->fromlist == NIL)
		return false;

	return true;
}

/*
 * has_nullable_targetlist
 *	  Check a subquery in the range table to see if all the non-junk
 *	  targetlist items are simple variables or strict functions of simple
 *	  variables (and, hence, will correctly go to NULL when examined above
 *	  the point of an outer join).
 *
 * NOTE: it would be correct (and useful) to ignore output columns that aren't
 * actually referenced by the enclosing query ... but we do not have that
 * information available at this point.
 */
static bool
has_nullable_targetlist(Query *subquery)
{
	ListCell   *l;

	foreach(l, subquery->targetList)
	{
		TargetEntry *tle = (TargetEntry *) lfirst(l);

		/* ignore resjunk columns */
		if (tle->resjunk)
			continue;

		/* Must contain a Var of current level */
		if (!contain_vars_of_level((Node *) tle->expr, 0))
			return false;

		/* Must not contain any non-strict constructs */
		if (contain_nonstrict_functions((Node *) tle->expr))
			return false;

		/* This one's OK, keep scanning */
	}
	return true;
}

/*
 * Helper routine for pull_up_subqueries: do ResolveNew on every expression
 * in the jointree, without changing the jointree structure itself.  Ugly,
 * but there's no other way...
 */
static void
resolvenew_in_jointree(Node *jtnode, int varno,
					   RangeTblEntry *rte, List *subtlist)
{
	if (jtnode == NULL)
		return;
	if (IsA(jtnode, RangeTblRef))
	{
		/* nothing to do here */
	}
	else if (IsA(jtnode, FromExpr))
	{
		FromExpr   *f = (FromExpr *) jtnode;
		ListCell   *l;

		foreach(l, f->fromlist)
			resolvenew_in_jointree(lfirst(l), varno, rte, subtlist);
		f->quals = ResolveNew(f->quals,
							  varno, 0, rte,
							  subtlist, CMD_SELECT, 0);
	}
	else if (IsA(jtnode, JoinExpr))
	{
		JoinExpr   *j = (JoinExpr *) jtnode;

		resolvenew_in_jointree(j->larg, varno, rte, subtlist);
		resolvenew_in_jointree(j->rarg, varno, rte, subtlist);
		j->quals = ResolveNew(j->quals,
							  varno, 0, rte,
							  subtlist, CMD_SELECT, 0);

		/*
		 * We don't bother to update the colvars list, since it won't be used
		 * again ...
		 */
	}
	else
		elog(ERROR, "unrecognized node type: %d",
			 (int) nodeTag(jtnode));
}

/*
 * reduce_outer_joins
 *		Attempt to reduce outer joins to plain inner joins.
 *
 * The idea here is that given a query like
 *		SELECT ... FROM a LEFT JOIN b ON (...) WHERE b.y = 42;
 * we can reduce the LEFT JOIN to a plain JOIN if the "=" operator in WHERE
 * is strict.  The strict operator will always return NULL, causing the outer
 * WHERE to fail, on any row where the LEFT JOIN filled in NULLs for b's
 * columns.  Therefore, there's no need for the join to produce null-extended
 * rows in the first place --- which makes it a plain join not an outer join.
 * (This scenario may not be very likely in a query written out by hand, but
 * it's reasonably likely when pushing quals down into complex views.)
 *
 * More generally, an outer join can be reduced in strength if there is a
 * strict qual above it in the qual tree that constrains a Var from the
 * nullable side of the join to be non-null.  (For FULL joins this applies
 * to each side separately.)
 *
 * To ease recognition of strict qual clauses, we require this routine to be
 * run after expression preprocessing (i.e., qual canonicalization and JOIN
 * alias-var expansion).
 */
void
reduce_outer_joins(PlannerInfo *root)
{
	reduce_outer_joins_state *state;

	/*
	 * To avoid doing strictness checks on more quals than necessary, we want
	 * to stop descending the jointree as soon as there are no outer joins
	 * below our current point.  This consideration forces a two-pass process.
	 * The first pass gathers information about which base rels appear below
	 * each side of each join clause, and about whether there are outer
	 * join(s) below each side of each join clause. The second pass examines
	 * qual clauses and changes join types as it descends the tree.
	 */
	state = reduce_outer_joins_pass1((Node *) root->parse->jointree);

	/* planner.c shouldn't have called me if no outer joins */
	if (state == NULL || !state->contains_outer)
		elog(ERROR, "so where are the outer joins?");

	reduce_outer_joins_pass2((Node *) root->parse->jointree,
							 state, root, NULL);
}

/*
 * reduce_outer_joins_pass1 - phase 1 data collection
 *
 * Returns a state node describing the given jointree node.
 */
static reduce_outer_joins_state *
reduce_outer_joins_pass1(Node *jtnode)
{
	reduce_outer_joins_state *result;

	result = (reduce_outer_joins_state *)
		palloc(sizeof(reduce_outer_joins_state));
	result->relids = NULL;
	result->contains_outer = false;
	result->sub_states = NIL;

	if (jtnode == NULL)
		return result;
	if (IsA(jtnode, RangeTblRef))
	{
		int			varno = ((RangeTblRef *) jtnode)->rtindex;

		result->relids = bms_make_singleton(varno);
	}
	else if (IsA(jtnode, FromExpr))
	{
		FromExpr   *f = (FromExpr *) jtnode;
		ListCell   *l;

		foreach(l, f->fromlist)
		{
			reduce_outer_joins_state *sub_state;

			sub_state = reduce_outer_joins_pass1(lfirst(l));
			result->relids = bms_add_members(result->relids,
											 sub_state->relids);
			result->contains_outer |= sub_state->contains_outer;
			result->sub_states = lappend(result->sub_states, sub_state);
		}
	}
	else if (IsA(jtnode, JoinExpr))
	{
		JoinExpr   *j = (JoinExpr *) jtnode;
		reduce_outer_joins_state *sub_state;

		/* join's own RT index is not wanted in result->relids */
		if (IS_OUTER_JOIN(j->jointype))
			result->contains_outer = true;

		sub_state = reduce_outer_joins_pass1(j->larg);
		result->relids = bms_add_members(result->relids,
										 sub_state->relids);
		result->contains_outer |= sub_state->contains_outer;
		result->sub_states = lappend(result->sub_states, sub_state);

		sub_state = reduce_outer_joins_pass1(j->rarg);
		result->relids = bms_add_members(result->relids,
										 sub_state->relids);
		result->contains_outer |= sub_state->contains_outer;
		result->sub_states = lappend(result->sub_states, sub_state);
	}
	else
		elog(ERROR, "unrecognized node type: %d",
			 (int) nodeTag(jtnode));
	return result;
}

/*
 * reduce_outer_joins_pass2 - phase 2 processing
 *
 *	jtnode: current jointree node
 *	state: state data collected by phase 1 for this node
 *	root: toplevel planner state
 *	nonnullable_rels: set of base relids forced non-null by upper quals
 */
static void
reduce_outer_joins_pass2(Node *jtnode,
						 reduce_outer_joins_state *state,
						 PlannerInfo *root,
						 Relids nonnullable_rels)
{
	/*
	 * pass 2 should never descend as far as an empty subnode or base rel,
	 * because it's only called on subtrees marked as contains_outer.
	 */
	if (jtnode == NULL)
		elog(ERROR, "reached empty jointree");
	if (IsA(jtnode, RangeTblRef))
		elog(ERROR, "reached base rel");
	else if (IsA(jtnode, FromExpr))
	{
		FromExpr   *f = (FromExpr *) jtnode;
		ListCell   *l;
		ListCell   *s;
		Relids		pass_nonnullable;

		/* Scan quals to see if we can add any nonnullability constraints */
		pass_nonnullable = find_nonnullable_rels(f->quals, true);
		pass_nonnullable = bms_add_members(pass_nonnullable,
										   nonnullable_rels);
		/* And recurse --- but only into interesting subtrees */
		Assert(list_length(f->fromlist) == list_length(state->sub_states));
		forboth(l, f->fromlist, s, state->sub_states)
		{
			reduce_outer_joins_state *sub_state = lfirst(s);

			if (sub_state->contains_outer)
				reduce_outer_joins_pass2(lfirst(l), sub_state, root,
										 pass_nonnullable);
		}
		bms_free(pass_nonnullable);
	}
	else if (IsA(jtnode, JoinExpr))
	{
		JoinExpr   *j = (JoinExpr *) jtnode;
		int			rtindex = j->rtindex;
		JoinType	jointype = j->jointype;
		reduce_outer_joins_state *left_state = linitial(state->sub_states);
		reduce_outer_joins_state *right_state = lsecond(state->sub_states);

		/* Can we simplify this join? */
		switch (jointype)
		{
			case JOIN_LEFT:
				if (bms_overlap(nonnullable_rels, right_state->relids))
					jointype = JOIN_INNER;
				break;
			case JOIN_RIGHT:
				if (bms_overlap(nonnullable_rels, left_state->relids))
					jointype = JOIN_INNER;
				break;
			case JOIN_FULL:
				if (bms_overlap(nonnullable_rels, left_state->relids))
				{
					if (bms_overlap(nonnullable_rels, right_state->relids))
						jointype = JOIN_INNER;
					else
						jointype = JOIN_LEFT;
				}
				else
				{
					if (bms_overlap(nonnullable_rels, right_state->relids))
						jointype = JOIN_RIGHT;
				}
				break;
			default:
				break;
		}
		if (jointype != j->jointype)
		{
			/* apply the change to both jointree node and RTE */
			RangeTblEntry *rte = rt_fetch(rtindex, root->parse->rtable);

			Assert(rte->rtekind == RTE_JOIN);
			Assert(rte->jointype == j->jointype);
			rte->jointype = j->jointype = jointype;
		}

		/* Only recurse if there's more to do below here */
		if (left_state->contains_outer || right_state->contains_outer)
		{
			Relids		local_nonnullable;
			Relids		pass_nonnullable;

			/*
			 * If this join is (now) inner, we can add any nonnullability
			 * constraints its quals provide to those we got from above. But
			 * if it is outer, we can only pass down the local constraints
			 * into the nullable side, because an outer join never eliminates
			 * any rows from its non-nullable side.  If it's a FULL join then
			 * it doesn't eliminate anything from either side.
			 */
			if (jointype != JOIN_FULL)
			{
				local_nonnullable = find_nonnullable_rels(j->quals, true);
				local_nonnullable = bms_add_members(local_nonnullable,
													nonnullable_rels);
			}
			else
				local_nonnullable = NULL;		/* no use in calculating it */

			if (left_state->contains_outer)
			{
				if (jointype == JOIN_INNER || jointype == JOIN_RIGHT)
					pass_nonnullable = local_nonnullable;
				else
					pass_nonnullable = nonnullable_rels;
				reduce_outer_joins_pass2(j->larg, left_state, root,
										 pass_nonnullable);
			}
			if (right_state->contains_outer)
			{
				if (jointype == JOIN_INNER || jointype == JOIN_LEFT)
					pass_nonnullable = local_nonnullable;
				else
					pass_nonnullable = nonnullable_rels;