rewritehandler.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

		sub_action->commandType != CMD_UTILITY)
	{
		sub_action = (Query *) ResolveNew((Node *) sub_action,
										  new_varno,
										  0,
										  rt_fetch(new_varno,
												   sub_action->rtable),
										  parsetree->targetList,
										  event,
										  current_varno);
		if (sub_action_ptr)
			*sub_action_ptr = sub_action;
		else
			rule_action = sub_action;
	}

	return rule_action;
}

/*
 * Copy the query's jointree list, and optionally attempt to remove any
 * occurrence of the given rt_index as a top-level join item (we do not look
 * for it within join items; this is OK because we are only expecting to find
 * it as an UPDATE or DELETE target relation, which will be at the top level
 * of the join).  Returns modified jointree list --- this is a separate copy
 * sharing no nodes with the original.
 */
static List *
adjustJoinTreeList(Query *parsetree, bool removert, int rt_index)
{
	List	   *newjointree = copyObject(parsetree->jointree->fromlist);
	ListCell   *l;

	if (removert)
	{
		foreach(l, newjointree)
		{
			RangeTblRef *rtr = lfirst(l);

			if (IsA(rtr, RangeTblRef) &&
				rtr->rtindex == rt_index)
			{
				newjointree = list_delete_ptr(newjointree, rtr);

				/*
				 * foreach is safe because we exit loop after list_delete...
				 */
				break;
			}
		}
	}
	return newjointree;
}


/*
 * rewriteTargetList - rewrite INSERT/UPDATE targetlist into standard form
 *
 * This has the following responsibilities:
 *
 * 1. For an INSERT, add tlist entries to compute default values for any
 * attributes that have defaults and are not assigned to in the given tlist.
 * (We do not insert anything for default-less attributes, however.  The
 * planner will later insert NULLs for them, but there's no reason to slow
 * down rewriter processing with extra tlist nodes.)  Also, for both INSERT
 * and UPDATE, replace explicit DEFAULT specifications with column default
 * expressions.
 *
 * 2. Merge multiple entries for the same target attribute, or declare error
 * if we can't.  Multiple entries are only allowed for INSERT/UPDATE of
 * portions of an array or record field, for example
 *			UPDATE table SET foo[2] = 42, foo[4] = 43;
 * We can merge such operations into a single assignment op.  Essentially,
 * the expression we want to produce in this case is like
 *		foo = array_set(array_set(foo, 2, 42), 4, 43)
 *
 * 3. Sort the tlist into standard order: non-junk fields in order by resno,
 * then junk fields (these in no particular order).
 *
 * We must do items 1 and 2 before firing rewrite rules, else rewritten
 * references to NEW.foo will produce wrong or incomplete results.	Item 3
 * is not needed for rewriting, but will be needed by the planner, and we
 * can do it essentially for free while handling items 1 and 2.
 */
static void
rewriteTargetList(Query *parsetree, Relation target_relation)
{
	CmdType		commandType = parsetree->commandType;
	TargetEntry **new_tles;
	List	   *new_tlist = NIL;
	List	   *junk_tlist = NIL;
	Form_pg_attribute att_tup;
	int			attrno,
				next_junk_attrno,
				numattrs;
	ListCell   *temp;

	/*
	 * We process the normal (non-junk) attributes by scanning the input tlist
	 * once and transferring TLEs into an array, then scanning the array to
	 * build an output tlist.  This avoids O(N^2) behavior for large numbers
	 * of attributes.
	 *
	 * Junk attributes are tossed into a separate list during the same tlist
	 * scan, then appended to the reconstructed tlist.
	 */
	numattrs = RelationGetNumberOfAttributes(target_relation);
	new_tles = (TargetEntry **) palloc0(numattrs * sizeof(TargetEntry *));
	next_junk_attrno = numattrs + 1;

	foreach(temp, parsetree->targetList)
	{
		TargetEntry *old_tle = (TargetEntry *) lfirst(temp);

		if (!old_tle->resjunk)
		{
			/* Normal attr: stash it into new_tles[] */
			attrno = old_tle->resno;
			if (attrno < 1 || attrno > numattrs)
				elog(ERROR, "bogus resno %d in targetlist", attrno);
			att_tup = target_relation->rd_att->attrs[attrno - 1];

			/* We can (and must) ignore deleted attributes */
			if (att_tup->attisdropped)
				continue;

			/* Merge with any prior assignment to same attribute */
			new_tles[attrno - 1] =
				process_matched_tle(old_tle,
									new_tles[attrno - 1],
									NameStr(att_tup->attname));
		}
		else
		{
			/*
			 * Copy all resjunk tlist entries to junk_tlist, and assign them
			 * resnos above the last real resno.
			 *
			 * Typical junk entries include ORDER BY or GROUP BY expressions
			 * (are these actually possible in an INSERT or UPDATE?), system
			 * attribute references, etc.
			 */

			/* Get the resno right, but don't copy unnecessarily */
			if (old_tle->resno != next_junk_attrno)
			{
				old_tle = flatCopyTargetEntry(old_tle);
				old_tle->resno = next_junk_attrno;
			}
			junk_tlist = lappend(junk_tlist, old_tle);
			next_junk_attrno++;
		}
	}

	for (attrno = 1; attrno <= numattrs; attrno++)
	{
		TargetEntry *new_tle = new_tles[attrno - 1];

		att_tup = target_relation->rd_att->attrs[attrno - 1];

		/* We can (and must) ignore deleted attributes */
		if (att_tup->attisdropped)
			continue;

		/*
		 * Handle the two cases where we need to insert a default expression:
		 * it's an INSERT and there's no tlist entry for the column, or the
		 * tlist entry is a DEFAULT placeholder node.
		 */
		if ((new_tle == NULL && commandType == CMD_INSERT) ||
			(new_tle && new_tle->expr && IsA(new_tle->expr, SetToDefault)))
		{
			Node	   *new_expr;

			new_expr = build_column_default(target_relation, attrno);

			/*
			 * If there is no default (ie, default is effectively NULL), we
			 * can omit the tlist entry in the INSERT case, since the planner
			 * can insert a NULL for itself, and there's no point in spending
			 * any more rewriter cycles on the entry.  But in the UPDATE case
			 * we've got to explicitly set the column to NULL.
			 */
			if (!new_expr)
			{
				if (commandType == CMD_INSERT)
					new_tle = NULL;
				else
				{
					new_expr = (Node *) makeConst(att_tup->atttypid,
												  att_tup->attlen,
												  (Datum) 0,
												  true, /* isnull */
												  att_tup->attbyval);
					/* this is to catch a NOT NULL domain constraint */
					new_expr = coerce_to_domain(new_expr,
												InvalidOid,
												att_tup->atttypid,
												COERCE_IMPLICIT_CAST,
												false,
												false);
				}
			}

			if (new_expr)
				new_tle = makeTargetEntry((Expr *) new_expr,
										  attrno,
										  pstrdup(NameStr(att_tup->attname)),
										  false);
		}

		if (new_tle)
			new_tlist = lappend(new_tlist, new_tle);
	}

	pfree(new_tles);

	parsetree->targetList = list_concat(new_tlist, junk_tlist);
}


/*
 * Convert a matched TLE from the original tlist into a correct new TLE.
 *
 * This routine detects and handles multiple assignments to the same target
 * attribute.  (The attribute name is needed only for error messages.)
 */
static TargetEntry *
process_matched_tle(TargetEntry *src_tle,
					TargetEntry *prior_tle,
					const char *attrName)
{
	TargetEntry *result;
	Node	   *src_expr;
	Node	   *prior_expr;
	Node	   *src_input;
	Node	   *prior_input;
	Node	   *priorbottom;
	Node	   *newexpr;

	if (prior_tle == NULL)
	{
		/*
		 * Normal case where this is the first assignment to the attribute.
		 */
		return src_tle;
	}

	/*----------
	 * Multiple assignments to same attribute.	Allow only if all are
	 * FieldStore or ArrayRef assignment operations.  This is a bit
	 * tricky because what we may actually be looking at is a nest of
	 * such nodes; consider
	 *		UPDATE tab SET col.fld1.subfld1 = x, col.fld2.subfld2 = y
	 * The two expressions produced by the parser will look like
	 *		FieldStore(col, fld1, FieldStore(placeholder, subfld1, x))
	 *		FieldStore(col, fld2, FieldStore(placeholder, subfld2, x))
	 * However, we can ignore the substructure and just consider the top
	 * FieldStore or ArrayRef from each assignment, because it works to
	 * combine these as
	 *		FieldStore(FieldStore(col, fld1,
	 *							  FieldStore(placeholder, subfld1, x)),
	 *				   fld2, FieldStore(placeholder, subfld2, x))
	 * Note the leftmost expression goes on the inside so that the
	 * assignments appear to occur left-to-right.
	 *
	 * For FieldStore, instead of nesting we can generate a single
	 * FieldStore with multiple target fields.	We must nest when
	 * ArrayRefs are involved though.
	 *----------
	 */
	src_expr = (Node *) src_tle->expr;
	prior_expr = (Node *) prior_tle->expr;
	src_input = get_assignment_input(src_expr);
	prior_input = get_assignment_input(prior_expr);
	if (src_input == NULL ||
		prior_input == NULL ||
		exprType(src_expr) != exprType(prior_expr))
		ereport(ERROR,
				(errcode(ERRCODE_SYNTAX_ERROR),
				 errmsg("multiple assignments to same column \"%s\"",
						attrName)));

	/*
	 * Prior TLE could be a nest of assignments if we do this more than once.
	 */
	priorbottom = prior_input;
	for (;;)
	{
		Node	   *newbottom = get_assignment_input(priorbottom);

		if (newbottom == NULL)
			break;				/* found the original Var reference */
		priorbottom = newbottom;
	}
	if (!equal(priorbottom, src_input))
		ereport(ERROR,
				(errcode(ERRCODE_SYNTAX_ERROR),
				 errmsg("multiple assignments to same column \"%s\"",
						attrName)));

	/*
	 * Looks OK to nest 'em.
	 */
	if (IsA(src_expr, FieldStore))
	{
		FieldStore *fstore = makeNode(FieldStore);

		if (IsA(prior_expr, FieldStore))
		{
			/* combine the two */
			memcpy(fstore, prior_expr, sizeof(FieldStore));
			fstore->newvals =
				list_concat(list_copy(((FieldStore *) prior_expr)->newvals),
							list_copy(((FieldStore *) src_expr)->newvals));
			fstore->fieldnums =
				list_concat(list_copy(((FieldStore *) prior_expr)->fieldnums),
							list_copy(((FieldStore *) src_expr)->fieldnums));
		}
		else
		{
			/* general case, just nest 'em */
			memcpy(fstore, src_expr, sizeof(FieldStore));
			fstore->arg = (Expr *) prior_expr;
		}
		newexpr = (Node *) fstore;
	}
	else if (IsA(src_expr, ArrayRef))
	{
		ArrayRef   *aref = makeNode(ArrayRef);

		memcpy(aref, src_expr, sizeof(ArrayRef));
		aref->refexpr = (Expr *) prior_expr;
		newexpr = (Node *) aref;
	}
	else
	{
		elog(ERROR, "can't happen");
		newexpr = NULL;
	}

	result = flatCopyTargetEntry(src_tle);
	result->expr = (Expr *) newexpr;
	return result;
}

/*
 * If node is an assignment node, return its input; else return NULL
 */
static Node *
get_assignment_input(Node *node)
{
	if (node == NULL)
		return NULL;
	if (IsA(node, FieldStore))
	{
		FieldStore *fstore = (FieldStore *) node;

		return (Node *) fstore->arg;
	}
	else if (IsA(node, ArrayRef))
	{
		ArrayRef   *aref = (ArrayRef *) node;

		if (aref->refassgnexpr == NULL)
			return NULL;
		return (Node *) aref->refexpr;
	}
	return NULL;
}

/*
 * Make an expression tree for the default value for a column.
 *
 * If there is no default, return a NULL instead.
 */
Node *
build_column_default(Relation rel, int attrno)
{
	TupleDesc	rd_att = rel->rd_att;
	Form_pg_attribute att_tup = rd_att->attrs[attrno - 1];
	Oid			atttype = att_tup->atttypid;
	int32		atttypmod = att_tup->atttypmod;
	Node	   *expr = NULL;
	Oid			exprtype;

	/*
	 * Scan to see if relation has a default for this column.
	 */
	if (rd_att->constr && rd_att->constr->num_defval > 0)
	{
		AttrDefault *defval = rd_att->constr->defval;
		int			ndef = rd_att->constr->num_defval;

		while (--ndef >= 0)
		{
			if (attrno == defval[ndef].adnum)
			{
				/*
				 * Found it, convert string representation to node tree.
				 */
				expr = stringToNode(defval[ndef].adbin);
				break;
			}
		}