如何在Sql中从一个表到另一个表获取项目总和

Question

如何在sql中从一个表到另一个表获取项的总和

Answer 1

使用联接和子查询

   select p.*,stock from theProduct p
    join ( select prodcode,sum(Qty) as stock from thePurchaseDetail group by prodcode) t
      on p.prodcode=t.prodcode

Answer 2

您可以使用APPLY：

select p.*, pp.stock 
from theProduct p cross apply
     (select sum(pp.qty) as stock 
      from thePurchaseDetail pp
      where pp.prodcode = p.prodcode
     ) pp;

您还可以将窗口功能与JOIN一起使用：

select p.*, sum(pp.qty) over (partition by p.prodcode) as stock
from theProduct p inner join
     thePurchaseDetail pp
     on pp.prodcode = p.prodcode;

Answer 3

如果tblPurchaseDetail表中缺少产品代码，您将退出联接

    select p.*
          ,t.stock 
     from tblProduct p
left join ( select prodcode
                  ,sum(Qty) as stock 
             from tblPurchaseDetail 
            group by prodcode
           ) t
      on p.prodcode=t.prodcode