Question

问题如下：对于每个活动，在一行上列出可获得一等奖，二等奖和三等奖的奖金。

所以我需要列出PRIZE表中的EVENT_ID。然后将有三个单独的列显示第一，第二和第三奖。

预期数据如下：

| event_id | First | Second | Third |    
|    101   |  120  |   60   |   30  |     
|    102   |  10   |   5    |   2   |     
|    103   |  100  |   60   |   40  |     
|    401   |  1000 |   500  |  250  |

表PRIZE具有列出的信息：

| Event_id      | Place      | Money      |    
| 101           | 1          | 120        |    
| 101           | 2          | 60         |    
| 101           | 3          | 30         |        
| 102           | 1          | 10         |    
| 102           | 2          | 5          |    
| 102           | 3          | 2          |    
| 103           | 1          | 100        |    
| 103           | 2          | 60         |   
| 103           | 3          | 40         |    
| 401           | 1          | 1000       |    
| 401           | 2          | 500        |    
| 401           | 3          | 250        |   
| 401           | 4          | 100        |    
| 401           | 5          | 50         |

到目前为止，我有：

SELECT event_id, money AS First, money AS Second, money AS Third

FROM PRIZE 

WHERE money IN

(SELECT money FROM PRIZE WHERE place=1 IN

(SELECT money FROM PRIZE WHERE place=2 IN

(SELECT money FROM PRIZE WHERE place=3

GROUP BY event_id)));

SQL只提供一个'OK'语句，并且不显示表。请帮忙吗？

Answer 1

我认为最简单的方法是使用substring_index()和group_concat()将它们全部放在一列中：

select event_id,
       substring_index(group_concat(money order by place), ',', 3)
from prize
group by event_id;

或者，对于三个单独的列，条件聚合也非常简单：

select event_id,
       max(case when place = 1 then money end) as first,
       max(case when place = 2 then money end) as second,
       max(case when place = 3 then money end) as third
from prize
group by event_id;

Answer 2

我的建议：

SELECT event_id,
(SELECT Money FROM prize WHERE event_id=p.event_id AND place=1) AS First,
(SELECT Money FROM prize WHERE event_id=p.event_id AND place=2) AS Second,
(SELECT Money FROM prize WHERE event_id=p.event_id AND place=3) AS Third,
FROM prize p

评论后编辑：添加：

GROUP BY event_id

MySQL子查询 - 在一行上显示结果

2 个答案: