rewritehandler.c

来自「PostgreSQL7.4.6 for Linux」· C语言 代码 · 共 1,349 行 · 第 1/3 页

	}

	/*
	 * Recurse into sublink subqueries, too.  But we already did the ones
	 * in the rtable.
	 */
	if (parsetree->hasSubLinks)
		query_tree_walker(parsetree, fireRIRonSubLink, (void *) activeRIRs,
						  QTW_IGNORE_RT_SUBQUERIES);

	/*
	 * If the query was marked having aggregates, check if this is still
	 * true after rewriting.  Ditto for sublinks.  Note there should be no
	 * aggs in the qual at this point.	(Does this code still do anything
	 * useful?	The view-becomes-subselect-in-FROM approach doesn't look
	 * like it could remove aggs or sublinks...)
	 */
	if (parsetree->hasAggs)
	{
		parsetree->hasAggs = checkExprHasAggs((Node *) parsetree);
		if (parsetree->hasAggs)
			if (checkExprHasAggs((Node *) parsetree->jointree))
				elog(ERROR, "failed to remove aggregates from qual");
	}
	if (parsetree->hasSubLinks)
		parsetree->hasSubLinks = checkExprHasSubLink((Node *) parsetree);

	return parsetree;
}


/*
 * Modify the given query by adding 'AND rule_qual IS NOT TRUE' to its
 * qualification.  This is used to generate suitable "else clauses" for
 * conditional INSTEAD rules.  (Unfortunately we must use "x IS NOT TRUE",
 * not just "NOT x" which the planner is much smarter about, else we will
 * do the wrong thing when the qual evaluates to NULL.)
 *
 * The rule_qual may contain references to OLD or NEW.	OLD references are
 * replaced by references to the specified rt_index (the relation that the
 * rule applies to).  NEW references are only possible for INSERT and UPDATE
 * queries on the relation itself, and so they should be replaced by copies
 * of the related entries in the query's own targetlist.
 */
static Query *
CopyAndAddInvertedQual(Query *parsetree,
					   Node *rule_qual,
					   int rt_index,
					   CmdType event)
{
	Query	   *new_tree = (Query *) copyObject(parsetree);
	Node	   *new_qual = (Node *) copyObject(rule_qual);

	/* Fix references to OLD */
	ChangeVarNodes(new_qual, PRS2_OLD_VARNO, rt_index, 0);
	/* Fix references to NEW */
	if (event == CMD_INSERT || event == CMD_UPDATE)
		new_qual = ResolveNew(new_qual,
							  PRS2_NEW_VARNO,
							  0,
							  parsetree->targetList,
							  event,
							  rt_index);
	/* And attach the fixed qual */
	AddInvertedQual(new_tree, new_qual);

	return new_tree;
}


/*
 *	fireRules -
 *	   Iterate through rule locks applying rules.
 *
 * Input arguments:
 *	parsetree - original query
 *	rt_index - RT index of result relation in original query
 *	event - type of rule event
 *	locks - list of rules to fire
 * Output arguments:
 *	*instead_flag - set TRUE if any unqualified INSTEAD rule is found
 *					(must be initialized to FALSE)
 *	*qual_product - filled with modified original query if any qualified
 *					INSTEAD rule is found (must be initialized to NULL)
 * Return value:
 *	list of rule actions adjusted for use with this query
 *
 * Qualified INSTEAD rules generate their action with the qualification
 * condition added.  They also generate a modified version of the original
 * query with the negated qualification added, so that it will run only for
 * rows that the qualified action doesn't act on.  (If there are multiple
 * qualified INSTEAD rules, we AND all the negated quals onto a single
 * modified original query.)  We won't execute the original, unmodified
 * query if we find either qualified or unqualified INSTEAD rules.	If
 * we find both, the modified original query is discarded too.
 */
static List *
fireRules(Query *parsetree,
		  int rt_index,
		  CmdType event,
		  List *locks,
		  bool *instead_flag,
		  Query **qual_product)
{
	List	   *results = NIL;
	List	   *i;

	foreach(i, locks)
	{
		RewriteRule *rule_lock = (RewriteRule *) lfirst(i);
		Node	   *event_qual = rule_lock->qual;
		List	   *actions = rule_lock->actions;
		QuerySource qsrc;
		List	   *r;

		/* Determine correct QuerySource value for actions */
		if (rule_lock->isInstead)
		{
			if (event_qual != NULL)
				qsrc = QSRC_QUAL_INSTEAD_RULE;
			else
			{
				qsrc = QSRC_INSTEAD_RULE;
				*instead_flag = true;	/* report unqualified INSTEAD */
			}
		}
		else
			qsrc = QSRC_NON_INSTEAD_RULE;

		if (qsrc == QSRC_QUAL_INSTEAD_RULE)
		{
			/*
			 * If there are INSTEAD rules with qualifications, the
			 * original query is still performed. But all the negated rule
			 * qualifications of the INSTEAD rules are added so it does
			 * its actions only in cases where the rule quals of all
			 * INSTEAD rules are false. Think of it as the default action
			 * in a case. We save this in *qual_product so RewriteQuery()
			 * can add it to the query list after we mangled it up enough.
			 *
			 * If we have already found an unqualified INSTEAD rule, then
			 * *qual_product won't be used, so don't bother building it.
			 */
			if (!*instead_flag)
			{
				if (*qual_product == NULL)
					*qual_product = parsetree;
				*qual_product = CopyAndAddInvertedQual(*qual_product,
													   event_qual,
													   rt_index,
													   event);
			}
		}

		/* Now process the rule's actions and add them to the result list */
		foreach(r, actions)
		{
			Query	   *rule_action = lfirst(r);

			if (rule_action->commandType == CMD_NOTHING)
				continue;

			rule_action = rewriteRuleAction(parsetree, rule_action,
											event_qual, rt_index, event);

			rule_action->querySource = qsrc;
			rule_action->canSetTag = false;		/* might change later */

			results = lappend(results, rule_action);
		}
	}

	return results;
}


/*
 * RewriteQuery -
 *	  rewrites the query and apply the rules again on the queries rewritten
 *
 * rewrite_events is a list of open query-rewrite actions, so we can detect
 * infinite recursion.
 */
static List *
RewriteQuery(Query *parsetree, List *rewrite_events)
{
	CmdType		event = parsetree->commandType;
	bool		instead = false;
	Query	   *qual_product = NULL;
	List	   *rewritten = NIL;

	/*
	 * If the statement is an update, insert or delete - fire rules on it.
	 *
	 * SELECT rules are handled later when we have all the queries that
	 * should get executed.  Also, utilities aren't rewritten at all (do
	 * we still need that check?)
	 */
	if (event != CMD_SELECT && event != CMD_UTILITY)
	{
		int			result_relation;
		RangeTblEntry *rt_entry;
		Relation	rt_entry_relation;
		List	   *locks;

		result_relation = parsetree->resultRelation;
		Assert(result_relation != 0);
		rt_entry = rt_fetch(result_relation, parsetree->rtable);
		Assert(rt_entry->rtekind == RTE_RELATION);

		/*
		 * This may well be the first access to the result relation during
		 * the current statement (it will be, if this Query was extracted
		 * from a rule or somehow got here other than via the parser).
		 * Therefore, grab the appropriate lock type for a result
		 * relation, and do not release it until end of transaction.  This
		 * protects the rewriter and planner against schema changes
		 * mid-query.
		 */
		rt_entry_relation = heap_open(rt_entry->relid, RowExclusiveLock);

		/*
		 * If it's an INSERT or UPDATE, rewrite the targetlist into
		 * standard form.  This will be needed by the planner anyway, and
		 * doing it now ensures that any references to NEW.field will
		 * behave sanely.
		 */
		if (event == CMD_INSERT || event == CMD_UPDATE)
			rewriteTargetList(parsetree, rt_entry_relation);

		/*
		 * Collect and apply the appropriate rules.
		 */
		locks = matchLocks(event, rt_entry_relation->rd_rules,
						   result_relation, parsetree);

		if (locks != NIL)
		{
			List	   *product_queries;

			product_queries = fireRules(parsetree,
										result_relation,
										event,
										locks,
										&instead,
										&qual_product);

			/*
			 * If we got any product queries, recursively rewrite them ---
			 * but first check for recursion!
			 */
			if (product_queries != NIL)
			{
				List	   *n;
				rewrite_event *rev;

				foreach(n, rewrite_events)
				{
					rev = (rewrite_event *) lfirst(n);
					if (rev->relation == RelationGetRelid(rt_entry_relation) &&
						rev->event == event)
						ereport(ERROR,
							 (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
							  errmsg("infinite recursion detected in rules for relation \"%s\"",
						   RelationGetRelationName(rt_entry_relation))));
				}

				rev = (rewrite_event *) palloc(sizeof(rewrite_event));
				rev->relation = RelationGetRelid(rt_entry_relation);
				rev->event = event;
				rewrite_events = lcons(rev, rewrite_events);

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

					newstuff = RewriteQuery(pt, rewrite_events);
					rewritten = nconc(rewritten, newstuff);
				}
			}
		}

		heap_close(rt_entry_relation, NoLock);	/* keep lock! */
	}

	/*
	 * For INSERTs, the original query is done first; for UPDATE/DELETE,
	 * it is done last.  This is needed 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 executions makes the deleted (and maybe the updated) tuples
	 * disappear so the scans for them in the rule actions cannot find
	 * them.
	 *
	 * If we found any unqualified INSTEAD, the original query is not done at
	 * all, in any form.  Otherwise, we add the modified form if qualified
	 * INSTEADs were found, else the unmodified form.
	 */
	if (!instead)
	{
		if (parsetree->commandType == CMD_INSERT)
		{
			if (qual_product != NULL)
				rewritten = lcons(qual_product, rewritten);
			else
				rewritten = lcons(parsetree, rewritten);
		}
		else
		{
			if (qual_product != NULL)
				rewritten = lappend(rewritten, qual_product);
			else
				rewritten = lappend(rewritten, parsetree);
		}
	}

	return rewritten;
}


/*
 * 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.
 */
List *
QueryRewrite(Query *parsetree)
{
	List	   *querylist;
	List	   *results = NIL;
	List	   *l;
	CmdType		origCmdType;
	bool		foundOriginalQuery;
	Query	   *lastInstead;

	/*
	 * Step 1
	 *
	 * Apply all non-SELECT rules possibly getting 0 or many queries
	 */
	querylist = RewriteQuery(parsetree, NIL);

	/*
	 * Step 2
	 *
	 * Apply all the RIR rules on each query
	 */
	foreach(l, querylist)
	{
		Query	   *query = (Query *) lfirst(l);

		query = fireRIRrules(query, NIL);

		/*
		 * If the query target was rewritten as a view, complain.
		 */
		if (query->resultRelation)
		{
			RangeTblEntry *rte = rt_fetch(query->resultRelation,
										  query->rtable);

			if (rte->rtekind == RTE_SUBQUERY)
			{
				switch (query->commandType)
				{
					case CMD_INSERT:
						ereport(ERROR,
								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
								 errmsg("cannot insert into a view"),
								 errhint("You need an unconditional ON INSERT DO INSTEAD rule.")));
						break;
					case CMD_UPDATE:
						ereport(ERROR,
								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
								 errmsg("cannot update a view"),
								 errhint("You need an unconditional ON UPDATE DO INSTEAD rule.")));
						break;
					case CMD_DELETE:
						ereport(ERROR,
								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
								 errmsg("cannot delete from a view"),
								 errhint("You need an unconditional ON DELETE DO INSTEAD rule.")));
						break;
					default:
						elog(ERROR, "unrecognized commandType: %d",
							 (int) query->commandType);
						break;
				}
			}
		}

		results = lappend(results, query);
	}

	/*
	 * Step 3
	 *
	 * Determine which, if any, of the resulting queries is supposed to set
	 * the command-result tag; and update the canSetTag fields
	 * accordingly.
	 *
	 * If the original query is still in the list, it sets the command tag.
	 * Otherwise, the last INSTEAD query of the same kind as the original
	 * is allowed to set the tag.  (Note these rules can leave us with no
	 * query setting the tag.  The tcop code has to cope with this by
	 * setting up a default tag based on the original un-rewritten query.)
	 *
	 * The Asserts verify that at most one query in the result list is marked
	 * canSetTag.  If we aren't checking asserts, we can fall out of the
	 * loop as soon as we find the original query.
	 */
	origCmdType = parsetree->commandType;
	foundOriginalQuery = false;
	lastInstead = NULL;

	foreach(l, results)
	{
		Query	   *query = (Query *) lfirst(l);

		if (query->querySource == QSRC_ORIGINAL)
		{
			Assert(query->canSetTag);
			Assert(!foundOriginalQuery);
			foundOriginalQuery = true;
#ifndef USE_ASSERT_CHECKING
			break;
#endif
		}
		else
		{
			Assert(!query->canSetTag);
			if (query->commandType == origCmdType &&
				(query->querySource == QSRC_INSTEAD_RULE ||
				 query->querySource == QSRC_QUAL_INSTEAD_RULE))
				lastInstead = query;
		}
	}

	if (!foundOriginalQuery && lastInstead != NULL)
		lastInstead->canSetTag = true;

	return results;
}