简单的sql语句问题,请指点.
3个表分别如下:
in: model,qty
out: model,qty
product: model,name,unit
怎样得到select model,name,unit,sum(in.qty),sum(out.qty),sum(in.qty)-sum(out.qty) from
.......where......?
如果where in.model=out.model and in.model=product.model的话,会丢失记录.
如果用group by的话,name,unit不能出现........请指点!!!