rewritehandler.c

关系型数据库 Postgresql 6.5.2

				else
					continue;
			}

			if (info->action == info->event &&
				info->event == CMD_SELECT)
				continue;

			/*
			 * Event Qualification forces copying of parsetree and
			 * splitting into two queries one w/rule_qual, one w/NOT
			 * rule_qual. Also add user query qual onto rule action
			 */
			qual = parsetree->qual;
			AddQual(info->rule_action, qual);

			if (info->rule_qual != NULL)
				AddQual(info->rule_action, info->rule_qual);

			/*--------------------------------------------------
			 * Step 2:
			 *	  Rewrite new.attribute w/ right hand side of target-list
			 *	  entry for appropriate field name in insert/update
			 *--------------------------------------------------
			 */
			if ((info->event == CMD_INSERT) || (info->event == CMD_UPDATE))
				FixNew(info, parsetree);

			/*--------------------------------------------------
			 * Step 3:
			 *	  rewriting due to retrieve rules
			 *--------------------------------------------------
			 */
			info->rule_action->rtable = info->rt;

			/*
			 * ProcessRetrieveQuery(info->rule_action, info->rt,
			 * &orig_instead_flag, TRUE);
			 */

			/*--------------------------------------------------
			 * Step 4
			 *	  Simplify? hey, no algorithm for simplification... let
			 *	  the planner do it.
			 *--------------------------------------------------
			 */
			results = lappend(results, info->rule_action);

			pfree(info);
		}

		/* ----------
		 * If this was an unqualified instead rule,
		 * throw away an eventually saved 'default' parsetree
		 * ----------
		 */
		if (event_qual == NULL && *instead_flag)
			*qual_products = NIL;
	}
	return results;
}



static List *
RewriteQuery(Query *parsetree, bool *instead_flag, List **qual_products)
{
	CmdType		event;
	List	   *product_queries = NIL;
	int			result_relation = 0;
	RangeTblEntry *rt_entry;
	Relation	rt_entry_relation = NULL;
	RuleLock   *rt_entry_locks = NULL;

	Assert(parsetree != NULL);

	event = parsetree->commandType;

	/*
	 * SELECT rules are handled later when we have all the queries that
	 * should get executed
	 */
	if (event == CMD_SELECT)
		return NIL;

	/*
	 * Utilities aren't rewritten at all - why is this here?
	 */
	if (event == CMD_UTILITY)
		return NIL;

	/*
	 * only for a delete may the targetlist be NULL
	 */
	if (event != CMD_DELETE)
		Assert(parsetree->targetList != NULL);

	result_relation = parsetree->resultRelation;

	/*
	 * the statement is an update, insert or delete - fire rules on it.
	 */
	rt_entry = rt_fetch(result_relation, parsetree->rtable);
	rt_entry_relation = heap_openr(rt_entry->relname);
	rt_entry_locks = rt_entry_relation->rd_rules;
	heap_close(rt_entry_relation);

	if (rt_entry_locks != NULL)
	{
		List	   *locks = matchLocks(event, rt_entry_locks, result_relation, parsetree);

		product_queries = fireRules(parsetree,
									result_relation,
									event,
									instead_flag,
									locks,
									qual_products);
	}

	return product_queries;

}


/*
 * to avoid infinite recursion, we restrict the number of times a query
 * can be rewritten. Detecting cycles is left for the reader as an excercise.
 */
#ifndef REWRITE_INVOKE_MAX
#define REWRITE_INVOKE_MAX		10
#endif

static int	numQueryRewriteInvoked = 0;

/*
 * deepRewriteQuery -
 *	  rewrites the query and apply the rules again on the queries rewritten
 */
static List *
deepRewriteQuery(Query *parsetree)
{
	List	   *n;
	List	   *rewritten = NIL;
	List	   *result = NIL;
	bool		instead;
	List	   *qual_products = NIL;



	if (++numQueryRewriteInvoked > REWRITE_INVOKE_MAX)
	{
		elog(ERROR, "query rewritten %d times, may contain cycles",
			 numQueryRewriteInvoked - 1);
	}

	instead = FALSE;
	result = RewriteQuery(parsetree, &instead, &qual_products);

	foreach(n, result)
	{
		Query	   *pt = lfirst(n);
		List	   *newstuff = NIL;

		newstuff = deepRewriteQuery(pt);
		if (newstuff != NIL)
			rewritten = nconc(rewritten, newstuff);
	}

	/* ----------
	 * qual_products are the original query with the negated
	 * rule qualification of an instead rule
	 * ----------
	 */
	if (qual_products != NIL)
		rewritten = nconc(rewritten, qual_products);

	/* ----------
	 * The original query is appended last if not instead
	 * because update and delete rule actions might not do
	 * anything if they are invoked after the update or
	 * delete is performed. The command counter increment
	 * between the query execution makes the deleted (and
	 * maybe the updated) tuples disappear so the scans
	 * for them in the rule actions cannot find them.
	 * ----------
	 */
	if (!instead)
		rewritten = lappend(rewritten, parsetree);

	return rewritten;
}


/*
 * QueryOneRewrite -
 *	  rewrite one query
 */
static List *
QueryRewriteOne(Query *parsetree)
{
	numQueryRewriteInvoked = 0;

	/*
	 * take a deep breath and apply all the rewrite rules - ay
	 */
	return deepRewriteQuery(parsetree);
}


/* ----------
 * RewritePreprocessQuery -
 *	adjust details in the parsetree, the rule system
 *	depends on
 * ----------
 */
static void
RewritePreprocessQuery(Query *parsetree)
{
	/* ----------
	 * if the query has a resultRelation, reassign the
	 * result domain numbers to the attribute numbers in the
	 * target relation. FixNew() depends on it when replacing
	 * *new* references in a rule action by the expressions
	 * from the rewritten query.
	 * resjunk targets are somewhat arbitrarily given a resno of 0;
	 * this is to prevent FixNew() from matching them to var nodes.
	 * ----------
	 */
	if (parsetree->resultRelation > 0)
	{
		RangeTblEntry *rte;
		Relation	rd;
		List	   *tl;

		rte = (RangeTblEntry *) nth(parsetree->resultRelation - 1,
									parsetree->rtable);
		rd = heap_openr(rte->relname);

		foreach(tl, parsetree->targetList)
		{
			TargetEntry *tle = (TargetEntry *) lfirst(tl);

			if (! tle->resdom->resjunk)
				tle->resdom->resno = attnameAttNum(rd, tle->resdom->resname);
			else
				tle->resdom->resno = 0;
		}

		heap_close(rd);
	}
}


/*
 * BasicQueryRewrite -
 *	  rewrite one query via query rewrite system, possibly returning 0
 *	  or many queries
 */
static List *
BasicQueryRewrite(Query *parsetree)
{
	List	   *querylist;
	List	   *results = NIL;
	List	   *l;
	Query	   *query;

	/*
	 * Step 1
	 *
	 * There still seems something broken with the resdom numbers so we
	 * reassign them first.
	 */
	RewritePreprocessQuery(parsetree);

	/*
	 * Step 2
	 *
	 * Apply all non-SELECT rules possibly getting 0 or many queries
	 */
	querylist = QueryRewriteOne(parsetree);

	/*
	 * Step 3
	 *
	 * Apply all the RIR rules on each query
	 */
	foreach(l, querylist)
	{
		query = fireRIRrules((Query *) lfirst(l));

		/*
		 * If the query was marked having aggregates, check if this is
		 * still true after rewriting. This check must get expanded when
		 * someday aggregates can appear somewhere else than in the
		 * targetlist or the having qual.
		 */
		if (query->hasAggs)
			query->hasAggs = checkQueryHasAggs((Node *) (query->targetList))
				| checkQueryHasAggs((Node *) (query->havingQual));
		query->hasSubLinks = checkQueryHasSubLink((Node *) (query->qual))
			| checkQueryHasSubLink((Node *) (query->havingQual));
		results = lappend(results, query);
	}
	return results;
}

/*
 * QueryRewrite -
 *	  Primary entry point to the query rewriter.
 *	  Rewrite one query via query rewrite system, possibly returning 0
 *	  or many queries.
 *
 * NOTE: The code in QueryRewrite was formerly in pg_parse_and_plan(), and was
 * moved here so that it would be invoked during EXPLAIN.  The division of
 * labor between this routine and BasicQueryRewrite is not obviously correct
 * ... at least not to me ... tgl 5/99.
 */
List *
QueryRewrite(Query *parsetree)
{
	List	   *rewritten,
			   *rewritten_item;

	/***S*I***/

	/*
	 * Rewrite Union, Intersect and Except Queries to normal Union Queries
	 * using IN and NOT IN subselects
	 */
	if (parsetree->intersectClause)
		parsetree = Except_Intersect_Rewrite(parsetree);

	/* Rewrite basic queries (retrieve, append, delete, replace) */
	rewritten = BasicQueryRewrite(parsetree);

	/*
	 * Rewrite the UNIONS.
	 */
	foreach(rewritten_item, rewritten)
	{
		Query	   *qry = (Query *) lfirst(rewritten_item);
		List	   *union_result = NIL;
		List	   *union_item;

		foreach(union_item, qry->unionClause)
		{
			union_result = nconc(union_result,
						BasicQueryRewrite((Query *) lfirst(union_item)));
		}
		qry->unionClause = union_result;
	}

	return rewritten;
}

/***S*I***/
/* This function takes two targetlists as arguments and checks if the
 * targetlists are compatible (i.e. both select for the same number of
 * attributes and the types are compatible */
static void
check_targetlists_are_compatible(List *prev_target, List *current_target)
{
	List	   *tl,
			   *next_target;
	int			prev_len = 0,
				next_len = 0;

	foreach(tl, prev_target)
		if (!((TargetEntry *) lfirst(tl))->resdom->resjunk)
		prev_len++;

	foreach(next_target, current_target)
		if (!((TargetEntry *) lfirst(next_target))->resdom->resjunk)
		next_len++;

	if (prev_len != next_len)
		elog(ERROR, "Each UNION | EXCEPT | INTERSECT query must have the same number of columns.");

	foreach(next_target, current_target)
	{
		Oid			itype;
		Oid			otype;

		otype = ((TargetEntry *) lfirst(prev_target))->resdom->restype;
		itype = ((TargetEntry *) lfirst(next_target))->resdom->restype;

		/* one or both is a NULL column? then don't convert... */
		if (otype == InvalidOid)
		{
			/* propagate a known type forward, if available */
			if (itype != InvalidOid)
				((TargetEntry *) lfirst(prev_target))->resdom->restype = itype;
#ifdef NOT_USED
			else
			{
				((TargetEntry *) lfirst(prev_target))->resdom->restype = UNKNOWNOID;
				((TargetEntry *) lfirst(next_target))->resdom->restype = UNKNOWNOID;
			}
#endif
		}
		else if (itype == InvalidOid)
		{
		}
		/* they don't match in type? then convert... */
		else if (itype != otype)
		{
			Node	   *expr;

			expr = ((TargetEntry *) lfirst(next_target))->expr;
			expr = CoerceTargetExpr(NULL, expr, itype, otype);
			if (expr == NULL)
			{
				elog(ERROR, "Unable to transform %s to %s"
					 "\n\tEach UNION | EXCEPT | INTERSECT clause must have compatible target types",
					 typeidTypeName(itype),
					 typeidTypeName(otype));
			}
			((TargetEntry *) lfirst(next_target))->expr = expr;
			((TargetEntry *) lfirst(next_target))->resdom->restype = otype;
		}

		/* both are UNKNOWN? then evaluate as text... */
		else if (itype == UNKNOWNOID)
		{
			((TargetEntry *) lfirst(next_target))->resdom->restype = TEXTOID;
			((TargetEntry *) lfirst(prev_target))->resdom->restype = TEXTOID;
		}
		prev_target = lnext(prev_target);
	}
}

/***S*I***/
/* Rewrites UNION INTERSECT and EXCEPT queries to semantiacally equivalent
 * queries that use IN and NOT IN subselects.
 *
 * The operator tree is attached to 'intersectClause' (see rule
 * 'SelectStmt' in gram.y) of the 'parsetree' given as an
 * argument. First we remember some clauses (the sortClause, the
 * unique flag etc.)  Then we translate the operator tree to DNF
 * (disjunctive normal form) by 'cnfify'. (Note that 'cnfify' produces
 * CNF but as we exchanged ANDs with ORs in function A_Expr_to_Expr()
 * earlier we get DNF after exchanging ANDs and ORs again in the
 * result.) Now we create a new query by evaluating the new operator
 * tree which is in DNF now. For every AND we create an entry in the
 * union list and for every OR we create an IN subselect. (NOT IN
 * subselects are created for OR NOT nodes). The first entry of the
 * union list is handed back but before that the remembered clauses
 * (sortClause etc) are attached to the new top Node (Note that the
 * new top Node can differ from the parsetree given as argument because of
 * the translation to DNF. That's why we have to remember the sortClause or
 * unique flag!) */
static Query *
Except_Intersect_Rewrite(Query *parsetree)
{

	SubLink    *n;
	Query	   *result,
			   *intersect_node;
	List	   *elist,
			   *intersect_list = NIL,
			   *intersect,
			   *intersectClause;
	List	   *union_list = NIL,
			   *sortClause;
	List	   *left_expr,
			   *right_expr,
			   *resnames = NIL;
	char	   *op,
			   *uniqueFlag,
			   *into;
	bool		isBinary,
				isPortal,
				isTemp;
	CmdType		commandType = CMD_SELECT;
	List	   *rtable_insert = NIL;

	List	   *prev_target = NIL;

	/*
	 * Remember the Resnames of the given parsetree's targetlist (these
	 * are the resnames of the first Select Statement of the query
	 * formulated by the user and he wants the columns named by these
	 * strings. The transformation to DNF can cause another Select
	 * Statment to be the top one which uses other names for its columns.
	 * Therefore we remeber the original names and attach them to the
	 * targetlist of the new topmost Node at the end of this function
	 */
	foreach(elist, parsetree->targetList)
	{
		TargetEntry *tent = (TargetEntry *) lfirst(elist);

		resnames = lappend(resnames, tent->resdom->resname);
	}

	/*
	 * If the Statement is an INSERT INTO ... (SELECT...) statement using
	 * UNIONs, INTERSECTs or EXCEPTs and the transformation to DNF makes
	 * another Node to the top node we have to transform the new top node
	 * to an INSERT node and the original INSERT node to a SELECT node
	 */
	if (parsetree->commandType == CMD_INSERT)
	{
		parsetree->commandType = CMD_SELECT;
		commandType = CMD_INSERT;
		parsetree->resultRelation = 0;

		/*
		 * The result relation ( = the one to insert into) has to be
		 * attached to the rtable list of the new top node
		 */
		rtable_insert = nth(length(parsetree->rtable) - 1, parsetree->rtable);
	}

	/*
	 * Save some items, to be able to attach them to the resulting top
	 * node at the end of the function
	 */
	sortClause = parsetree->sortClause;
	uniqueFlag = parsetree->uniqueFlag;
	into = parsetree->into;
	isBinary = parsetree->isBinary;
	isPortal = parsetree->isPortal;
	isTemp = parsetree->isTemp;

	/*
	 * The operator tree attached to parsetree->intersectClause is still
	 * 'raw' ( = the leaf nodes are still SelectStmt nodes instead of
	 * Query nodes) So step through the tree and transform the nodes using
	 * parse_analyze().
	 *
	 * The parsetree (given as an argument to Except_Intersect_Rewrite()) has
	 * already been transformed and transforming it again would cause
	 * troubles.  So we give the 'raw' version (of the cooked parsetree)
	 * to the function to prevent an additional transformation. Instead we
	 * hand back the 'cooked' version also given as an argument to
	 * intersect_tree_analyze()
	 */
	intersectClause =
		(List *) intersect_tree_analyze((Node *) parsetree->intersectClause,
								 (Node *) lfirst(parsetree->unionClause),
										(Node *) parsetree);

	/* intersectClause is no longer needed so set it to NIL */
	parsetree->intersectClause = NIL;

	/*
	 * unionClause will be needed later on but the list it delivered is no
	 * longer needed, so set it to NIL
	 */
	parsetree->unionClause = NIL;

	/*
	 * Transform the operator tree to DNF (remember ANDs and ORs have been
	 * exchanged, that's why we get DNF by using cnfify)
	 *
	 * After the call, explicit ANDs are removed and all AND operands are
	 * simply items in the intersectClause list
	 */
	intersectClause = cnfify((Expr *) intersectClause, true);

	/*
	 * For every entry of the intersectClause list we generate one entry
	 * in the union_list
	 */
	foreach(intersect, intersectClause)
	{

		/*
		 * for every OR we create an IN subselect and for every OR NOT we
		 * create a NOT IN subselect, so first extract all the Select
		 * Query nodes from the tree (that contains only OR or OR NOTs any
		 * more because we did a transformation to DNF
		 *
		 * There must be at least one node that is not negated (i.e. just OR
		 * and not OR NOT) and this node will be the first in the list
		 * returned
		 */
		intersect_list = NIL;
		create_intersect_list((Node *) lfirst(intersect), &intersect_list);

		/*
		 * This one will become the Select Query node, all other nodes are
		 * transformed into subselects under this node!
		 */
		intersect_node = (Query *) lfirst(intersect_list);
		intersect_list = lnext(intersect_list);

		/*
		 * Check if all Select Statements use the same number of
		 * attributes and if all corresponding attributes are of the same
		 * type
		 */
		if (prev_targe