[求助]请教一条sql语句?
这里有表j_stock,j_clothing,d_inventory,但我不知道not in在select语句中是什么意思?还有select语句的嵌套又如何解释,第二个select语句中的union起什么作用?select * from j_stock where clothingid not in (select clothingid from j_clothing)
union select * from d_inventorysub where clothingid not in (select clothingid from j_clothing)
想请教各位高手指点迷津!在此感激不尽。