Question

我必须使用SQL子查询来回答以下问题。

原始表是奖

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

问题是：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。按event_id排序。表格的第一行如下： event_id第一个第二个第三个 101 120 60 30 .....

我的回答是：使用horsedb;

SELECT event_id,
(SELECT money FROM prize WHERE place = '1' AND event_id = prize.event_id) AS 'First',
(SELECT money FROM prize WHERE place = '2' AND event_id = prize.event_id) AS 'Second',
(SELECT money FROM prize WHERE place = '3' AND event_id = prize.event_id) AS 'Third'
FROM prize
ORDER BY event_id;

但答案有1024（返回多行）错误。我试过IN，任何结果都不好请帮助，谢谢

Answer 1

以下是查询：

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

如果你需要它可以使用sqlfiddle： http://sqlfiddle.com/#!2/aa691/1/0

Answer 2

关于输出应该是什么样的问题不明确，但这里有一个建议：尝试使用GROUP BY和GROUP_CONCAT。例如：

SELECT event_id, 
       GROUP_CONCAT(place ORDER BY place) AS place,
       GROUP_CONCAT(money ORDER BY place) AS money
FROM prize
GROUP BY event_id;

给出：

+----------+-----------+---------------------+
| event_id | place     | money               |
+----------+-----------+---------------------+
|      101 | 1,2,3     | 120,60,30           |
|      102 | 1,2,3     | 10,5,2              |
|      103 | 1,2,3     | 100,60,40           |
|      401 | 1,2,3,4,5 | 1000,500,250,100,50 |
+----------+-----------+---------------------+

在一条线上显示一等奖，二等奖和三等奖

2 个答案: