initsplan.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

			else if (bms_equal(outerjoin_nonnullable, qualscope))
			{
				/* FULL JOIN (above tests cannot match in this case) */
				root->full_join_clauses = lappend(root->full_join_clauses,
												  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(PlannerInfo *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;
	ListCell   *itm;
	Oid			ltype,
				rtype;
	Operator	eq_operator;
	Form_pg_operator pgopform;
	Expr	   *clause;

	/* Get set of relids referenced in the two expressions */
	relids = bms_union(item1_relids, item2_relids);
	membership = bms_membership(relids);

	/*
	 * generate_implied_equalities() shouldn't call me on two constants.
	 */
	Assert(membership != BMS_EMPTY_SET);

	/*
	 * If the exprs involve a single rel, we need to look at that rel's
	 * baserestrictinfo list.  If multiple rels, we can scan the joininfo list
	 * of any of 'em.
	 */
	if (membership == BMS_SINGLETON)
	{
		rel1 = find_base_rel(root, bms_singleton_member(relids));
		restrictlist = rel1->baserestrictinfo;
	}
	else
	{
		Relids		other_rels;
		int			first_rel;

		/* Copy relids, find and remove one member */
		other_rels = bms_copy(relids);
		first_rel = bms_first_member(other_rels);
		bms_free(other_rels);

		rel1 = find_base_rel(root, first_rel);
		restrictlist = rel1->joininfo;
	}

	/*
	 * Scan to see if equality is already known.  If so, we're done in the add
	 * case, and done after removing it in the delete case.
	 */
	foreach(itm, restrictlist)
	{
		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(itm);
		Node	   *left,
				   *right;

		if (restrictinfo->mergejoinoperator == InvalidOid)
			continue;			/* ignore non-mergejoinable clauses */
		/* We now know the restrictinfo clause is a binary opclause */
		left = get_leftop(restrictinfo->clause);
		right = get_rightop(restrictinfo->clause);
		if ((equal(item1, left) && equal(item2, right)) ||
			(equal(item2, left) && equal(item1, right)))
		{
			/* found a matching clause */
			if (delete_it)
			{
				if (membership == BMS_SINGLETON)
				{
					/* delete it from local restrictinfo list */
					rel1->baserestrictinfo = list_delete_ptr(rel1->baserestrictinfo,
															 restrictinfo);
				}
				else
				{
					/* let joininfo.c do it */
					remove_join_clause_from_rels(root, restrictinfo, relids);
				}
			}
			return;				/* done */
		}
	}

	/* Didn't find it.  Done if deletion requested */
	if (delete_it)
		return;

	/*
	 * This equality is new information, so construct a clause representing it
	 * to add to the query data structures.
	 */
	ltype = exprType(item1);
	rtype = exprType(item2);
	eq_operator = compatible_oper(list_make1(makeString("=")),
								  ltype, rtype, true);
	if (!HeapTupleIsValid(eq_operator))
	{
		/*
		 * Would it be safe to just not add the equality to the query if we
		 * have no suitable equality operator for the combination of
		 * datatypes?  NO, because sortkey selection may screw up anyway.
		 */
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_FUNCTION),
		errmsg("could not identify an equality operator for types %s and %s",
			   format_type_be(ltype), format_type_be(rtype))));
	}
	pgopform = (Form_pg_operator) GETSTRUCT(eq_operator);

	/*
	 * Let's just make sure this appears to be a compatible operator.
	 */
	if (pgopform->oprlsortop != sortop1 ||
		pgopform->oprrsortop != sortop2 ||
		pgopform->oprresult != BOOLOID)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
				 errmsg("equality operator for types %s and %s should be merge-joinable, but isn't",
						format_type_be(ltype), format_type_be(rtype))));

	/*
	 * Now we can 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(oprid(eq_operator),	/* opno */
						   BOOLOID,		/* opresulttype */
						   false,		/* opretset */
						   (Expr *) copyObject(item1),
						   (Expr *) copyObject(item2));

	ReleaseSysCache(eq_operator);

	/*
	 * Push the new clause into all the appropriate restrictinfo lists.
	 *
	 * Note: we mark the qual "pushed down" to ensure that it can never be
	 * taken for an original JOIN/ON clause.
	 */
	distribute_qual_to_rels(root, (Node *) clause,
							true, true, false, NULL, relids);
}

/*
 * qual_is_redundant
 *	  Detect whether an implied-equality qual that turns out to be a
 *	  restriction clause for a single base relation is redundant with
 *	  already-known restriction clauses for that rel.  This occurs with,
 *	  for example,
 *				SELECT * FROM tab WHERE f1 = f2 AND f2 = f3;
 *	  We need to suppress the redundant condition to avoid computing
 *	  too-small selectivity, not to mention wasting time at execution.
 *
 * Note: quals of the form "var = const" are never considered redundant,
 * only those of the form "var = var".	This is needed because when we
 * have constants in an implied-equality set, we use a different strategy
 * that suppresses all "var = var" deductions.	We must therefore keep
 * all the "var = const" quals.
 */
static bool
qual_is_redundant(PlannerInfo *root,
				  RestrictInfo *restrictinfo,
				  List *restrictlist)
{
	Node	   *newleft;
	Node	   *newright;
	List	   *oldquals;
	ListCell   *olditem;
	List	   *equalexprs;
	bool		someadded;

	/* Never redundant unless vars appear on both sides */
	if (bms_is_empty(restrictinfo->left_relids) ||
		bms_is_empty(restrictinfo->right_relids))
		return false;

	newleft = get_leftop(restrictinfo->clause);
	newright = get_rightop(restrictinfo->clause);

	/*
	 * Set cached pathkeys.  NB: it is okay to do this now because this
	 * routine is only invoked while we are generating implied equalities.
	 * Therefore, the equi_key_list is already complete and so we can
	 * correctly determine canonical pathkeys.
	 */
	cache_mergeclause_pathkeys(root, restrictinfo);
	/* If different, say "not redundant" (should never happen) */
	if (restrictinfo->left_pathkey != restrictinfo->right_pathkey)
		return false;

	/*
	 * Scan existing quals to find those referencing same pathkeys. Usually
	 * there will be few, if any, so build a list of just the interesting
	 * ones.
	 */
	oldquals = NIL;
	foreach(olditem, restrictlist)
	{
		RestrictInfo *oldrinfo = (RestrictInfo *) lfirst(olditem);

		if (oldrinfo->mergejoinoperator != InvalidOid)
		{
			cache_mergeclause_pathkeys(root, oldrinfo);
			if (restrictinfo->left_pathkey == oldrinfo->left_pathkey &&
				restrictinfo->right_pathkey == oldrinfo->right_pathkey)
				oldquals = lcons(oldrinfo, oldquals);
		}
	}
	if (oldquals == NIL)
		return false;

	/*
	 * Now, we want to develop a list of exprs that are known equal to the
	 * left side of the new qual.  We traverse the old-quals list repeatedly
	 * to transitively expand the exprs list.  If at any point we find we can
	 * reach the right-side expr of the new qual, we are done.	We give up
	 * when we can't expand the equalexprs list any more.
	 */
	equalexprs = list_make1(newleft);
	do
	{
		someadded = false;
		/* cannot use foreach here because of possible list_delete */
		olditem = list_head(oldquals);
		while (olditem)
		{
			RestrictInfo *oldrinfo = (RestrictInfo *) lfirst(olditem);
			Node	   *oldleft = get_leftop(oldrinfo->clause);
			Node	   *oldright = get_rightop(oldrinfo->clause);
			Node	   *newguy = NULL;

			/* must advance olditem before list_delete possibly pfree's it */
			olditem = lnext(olditem);

			if (list_member(equalexprs, oldleft))
				newguy = oldright;
			else if (list_member(equalexprs, oldright))
				newguy = oldleft;
			else
				continue;
			if (equal(newguy, newright))
				return true;	/* we proved new clause is redundant */
			equalexprs = lcons(newguy, equalexprs);
			someadded = true;

			/*
			 * Remove this qual from list, since we don't need it anymore.
			 */
			oldquals = list_delete_ptr(oldquals, oldrinfo);
		}
	} while (someadded);

	return false;				/* it's not redundant */
}


/*****************************************************************************
 *
 *	 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,
				leftOp,
				rightOp;

	if (!is_opclause(clause))
		return;
	if (list_length(((OpExpr *) clause)->args) != 2)
		return;

	opno = ((OpExpr *) clause)->opno;

	if (op_mergejoinable(opno,
						 &leftOp,
						 &rightOp) &&
		!contain_volatile_functions((Node *) clause))
	{
		restrictinfo->mergejoinoperator = opno;
		restrictinfo->left_sortop = leftOp;
		restrictinfo->right_sortop = rightOp;
	}
}

/*
 * 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;

	if (!is_opclause(clause))
		return;
	if (list_length(((OpExpr *) clause)->args) != 2)
		return;

	opno = ((OpExpr *) clause)->opno;

	if (op_hashjoinable(opno) &&
		!contain_volatile_functions((Node *) clause))
		restrictinfo->hashjoinoperator = opno;
}