数据库问题--null空值
我通过数据库左连接去减另一个表的值,但可能另一个表的值为空值,这时数据就出不来了例如:select bookreport.bookid,(bookreport.bookcount-storebook.bookcount) as bookcount from bookreport left outer join storebook on bookreport.bookid=storebook.bookid
但如果说storebook.bookcount为null值,则bookcount显是却为空,而我的bookreport.bookcount一定有数据。