* vinita vigine Murugiah > I'm using ver 3:23:49 & 3:23:53, I thought > "A LEFT JOIN B USING (c)" is Identical to "A LEFT JOIN B ON A.c = B.c"
I think it is... > It seems it is NOT the case if you are joining more that ONE table & one > of them is EMPTY. Please see the following Example [... excelent examples snipped for bandwith preservation...] > mysql> select * from room LEFT JOIN roomLock USING (roomNum) LEFT JOIN > roomOwner USING (roomNum) [...] > I would expect the same result if I Left join the roomOwner followed by > roomNum, BUT IT IS NOT > Is it a bug?? or my expectation is wrong?? It's your expectations... notice that the roomOwner.roomNum column is NULL. USING relates to the immediately preceding table. [...] > mysql> select * from room LEFT JOIN roomOwner ON room.roomNum = > roomOwner.roomNum > -> LEFT JOIN roomLock ON room.roomNum = roomLock.roomNum; This is not the same... instead of "LEFT JOIN roomLock ON room.roomNum = roomLock.roomNum" you would have to use "LEFT JOIN roomLock ON roomOwner.roomNum = roomLock.roomNum" to get the same behaviour as with USING(roomNum). -- Roger --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
