Question

我是SQL的新手，所以尝试了很多之后，我找不到合适的解决方案在Stackoverflow上。这就是为什么我发表我的问题。[可能是重复的问题]

我有2个表T1和T2。给出的结构如下：

Tables:
T1:
Task     Category     Estimated_Cost
 1        9100           100
 2        9100            15
 3        9100             6
 4        9200             8
 5        9200            11

T2:
Voucher    Task        Actual_Cost
  1          1            10
  2          1            20
  3          1            15
  4          2            32
  5          4             8
  6          5             3
  7          5             4

我希望结果为：

Category     Estimated_Cost     Actual_Cost
 9100           121                77
 9200            19                15

对此使用哪个查询？

Answer 1

嗯。。。这是一种方法：

select category, sum(estimated_cost) as estimated_cost, sum(actual_cost) as actual_cost
from ((select t1.category, t1.estimated_cost, 0 as actual_cost
       from t1
      ) union all
      (select t1.category, 0, t2.actual_cost
       from t2 join
            t1
            on t1.task = t2.task
      )
     ) cc
group by category;

Answer 2

select *
from
     (select t1.category, sum(t1.estimated_cost) estimated_cost
      from t1
      group by t1.category
     ) A
join
     (select t1.category, sum(t2.actual_cost) actual_cost
      from t2 
      join t1 on t1.task = t2.task
      group by t1.category
     ) B
on A.category = B.category

根据其他表中使用的外键访问表中的所有行

2 个答案: