多表求和

1.有一個使用者表users，兩個文章表articles_1,articles_2。
如果得出articles_1中的tickets欄位以及articles_2中的tickets欄位的和。條件是與users中userid相同的記錄。

 

select  userid,
articlesCount = isnull((select sum(A1.tickets) from articles_1 A1 where A1.userid = U.userid),0) +
isnull((select sum(A2.tickets) from articles_2 A2 where A2.userid = U.userid),0)
from users U

可以查出users表中所有user的articles的數量，列articlesCount的值就是這個和！

 

2.select
  (select count(*) from a)as info_1,
  (select sum(Hits) from a) as info_2,
  (select count(*) from b) as info_3,
  (select count(*) from c) as info_4