如何分組結果從一個列在MySQL

Question

檢索到的我想做些事情是這樣的：如果你想一排

SELECT sum(quantity) 
FROM orders 
WHERE order_code between **code1** and **code2** as group1 
and order_code between **code3** and **code4** as group2 
and order_code between **code5** and **code6** as group3 

Answer 1

有三列：

SELECT SUM(IF(order_code BETWEEN ... AND ..., quantity, 0)), -- group1 
     SUM(IF(order_code BETWEEN ... AND ..., quantity, 0)), -- group2 
     SUM(IF(order_code BETWEEN ... AND ..., quantity, 0)) -- group3 
    FROM orders 
; 

如果你想要一個列與三行：

SELECT group_number, 
     SUM(quantity) 
    FROM (SELECT quantity, 
       CASE WHEN order_code BETWEEN ... AND ... THEN 1 -- group1 
        WHEN order_code BETWEEN ... AND ... THEN 2 -- group2 
        WHEN order_code BETWEEN ... AND ... THEN 3 -- group3 
        ELSE NULL 
       END AS group_number 
      FROM orders 
     ) AS t 
WHERE group_number IS NOT NULL 
GROUP 
    BY group_number 
; 

（子查詢實際上並不是必要的，但我認爲它使得它更清楚發生了什麼）。