Case 语句中的 Sum 函数

Question

我正在处理一个查询，我需要在各种条件下找到总和。现在我的查询是：

select
sum(case when condition then A_amount end) as S_A_amount,
sum(case when condition then B_amount end) as S_B_amount

但在第三种情况下，我还需要在 When 条件下使用 sum 函数

sum(case when sum(C_amount)>3 then 6 else sum(C_amount) end) as S_C_amount
from table A group by item

我无法实现第三个条件。我收到not a single group-by 错误。

Answer 1

如果没有一些示例数据，很难确定您要达到的目标，但在 same 组中使用 SUM(SUM(value)) 不会与仅使用 SUM(value) 产生不同的结果，所以它看来您可以使用：

SQL Fiddle

Oracle 11g R2 架构设置：

CREATE TABLE A ( item, A_Amount, B_Amount, C_Amount, cond ) AS
SELECT 1, 1, 1, 1, 1 FROM DUAL UNION ALL
SELECT 1, 1, 1, 1, 2 FROM DUAL UNION ALL
SELECT 1, 1, 1, 1, 3 FROM DUAL UNION ALL
SELECT 1, 1, 1, 0, 4 FROM DUAL UNION ALL
SELECT 2, 2, 2, 2, 1 FROM DUAL UNION ALL
SELECT 2, 2, 2, 2, 2 FROM DUAL UNION ALL
SELECT 2, 2, 2, 2, 3 FROM DUAL UNION ALL
SELECT 2, 2, 2, 2, 4 FROM DUAL;

查询 1：

SELECT item,
       SUM( CASE WHEN cond > 0 THEN A_amount END ) AS S_A_amount,
       SUM( CASE WHEN cond > 0 THEN B_amount END ) AS S_B_amount,
       CASE WHEN SUM(C_amount)>3 THEN 6 ELSE SUM(C_amount) END AS S_C_amount
FROM   A
GROUP BY item

Results：

| ITEM | S_A_AMOUNT | S_B_AMOUNT | S_C_AMOUNT |
|------|------------|------------|------------|
|    1 |          4 |          4 |          3 |
|    2 |          8 |          8 |          6 |

Answer 2

这是你需要的吗？

select case
          when sum_c_amount > 3 then
           6
          else
           sum_c_amount
       end as s_c_amount
  from (select sum(c_amount) as sum_c_amount
          from table a
         group by item) 

Answer 3

将现有查询移动到子查询中，并将案例表达式逻辑放在外部查询层中，例如

select
       d.*
     , case when S_C_amount > 3 then 6 else S_C_amount end
from (
      select
            item
          , sum(case when condition then A_amount end) as S_A_amount
          , sum(case when condition then B_amount end) as S_B_amount
          , sum(case when condition then C_amount end) as S_C_amount
      from t
      group by item
      ) d

Answer 4

我会这样做：

SELECT item,
       sum(case when condition then A_amount end) as S_A_amount,
       sum(case when condition then B_amount end) as S_B_amount,
       sum(case when s_c_amount>3 then 6 else s_c_amount end) as S_C_amount
 FROM (select item,
              A_amount,
              B_amount,
              sum(C_amount) over (partition by item) as s_c_amount
         from table A)
GROUP BY item