Mysql：在組中添加條件

Question

通過在查詢中使用group by source子句，得到以下結果。

Source No_of_users 
    1   2 
    2   7 
    3   3 
    4   34 
    5   21 

我怎樣才能像一羣源即輸出的一些值：

Source No_of_users 
    1+2   9 
    3+5   24 
    4   34 

需要建議。

Answer 1

是，使用聯合像：

SELECT SUM(no_of_users) AS some_sum from some_table where source in (1,2,3) 
UNION 
SELECT SUM(no_of_users) AS some_sum from some_table where source in (4,5,6) 
UNION 
SELECT SUM(no_of_users) AS some_sum from some_table where source in (6,7,8) 

Answer 2

Try This...... 

with cte as (
    select 
     case Name 
      when '2' then '1' 
      when '5' then '3' 
       //add more combinations .... 
      else Name 
     end as Name 
    from table 
) 
select Name, count(*) 
from cte 
group by Name 

Answer 3

這可以通過使用一個嵌套SELECT到Source柱強制爲適當的值，則分組生成的行來實現：

SELECT Source, 
     SUM(No_of_users) 
    FROM (SELECT CASE 
        WHEN Source = 1 THEN '1+2' 
        WHEN Source = 2 THEN '1+2' 
        WHEN Source = 3 THEN '3+5' 
        WHEN Source = 5 THEN '3+5' 
        ELSE Source 
       END AS Source, 
       No_of_users 
     FROM `Table`) AS A 
    GROUP BY Source 

SQL提琴可用here來演示。

Answer 4

在MySQL中，你可以這樣做：

SELECT (CASE WHEN Source in (1, 2) THEN '1+2' 
      WHEN Source in (3, 5) THEN '3+5' 
      ELSE Source 
     END) as Source, 
     SUM(No_of_users) as No_of_users 
FROM `Table` t 
GROUP BY Source 
ORDER BY Source;