SQL查询来计算每个产品组合

Question

我需要SQL查询来计算出每个产品组合。

我有一个分配给这三个类别的三个产品类别（游戏，配件，升级）和产品：

+----+------------+-----------+------------+ 
| id | category | product | prod_code | 
+----+------------+-----------+------------+ 
| 1 | game  | GTA  |  100 | 
| 2 | game  | GTA1  |  200 | 
| 3 | game  | GTA2  |  300 | 
| 4 | accessory | Play Pad |  400 | 
| 5 | accessory | Xbox Pad |  500 | 
| 6 | upgrade | Memory |  600 | 
| 6 | upgrade | drive  |  700 | 
+----+------------+-----------+------------+ 

我想借此从每个类别中的一个产品，制定出每一个组合：

+----+--------------+ 
| id | combinations | 
+----+--------------+ 
| 1 | 100,400,600 | 
| 2 | 100,500,600 | 
| 3 | 100,400,700 | 
| 4 | 100,500,700 | 
| ? | etc   | 
+----+--------------+ 

我该怎么做呢？

由于提前，司徒

Answer 1

使用CROSS JOIN：

SELECT CONCAT(t1.[prod_code], ',', 
       t2.[prod_code], ',', 
       t3.[prod_code]) 
FROM (
    SELECT [prod_code] 
    FROM mytable 
    WHERE category = 'game') AS t1 
CROSS JOIN ( 
    SELECT [prod_code] 
    FROM mytable 
    WHERE category = 'accessory') AS t2 
CROSS JOIN (
    SELECT [prod_code] 
    FROM mytable 
    WHERE category = 'upgrade') AS t3 
ORDER BY t1.[prod_code], t2.[prod_code], t3.[prod_code] 

派生表的CROSS JOIN，一个用于每个类别，产生以下笛卡尔乘积：'game' products X 'accessory' products X 'upgrade' products

Demo here