Not IN问题
Exists，not Exists，in，not in
例如：
DELETE FROM YSHA WHERE NOT EXISTS(SELECT 1 FROM YSHB B WHERE YSHA.code=b.code )
等同于
DELETE A FROM YSHA A LEFT JOIN YSHB B ON A.code=b.code WHERE b.code is NULL
Oracle，用left join 替代 exists ,not exists,in , not in，提高效率
原文：http://www.cnblogs.com/alsf/p/7831420.html