Question

所以我有一个看起来像这样的表:(称为PRIZE）

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

我试图回答这个问题：＆＃39;对于每个活动，在一行上列出可用于第一，第二和第三名的奖金。按event_id分组。

例如。将出现一行结果：

Event_id   First   Second   Third
101         120      60      30

到目前为止我已经知道了这一点：

SELECT Event_id, Money AS 'First' 
FROM PRIZE 
WHERE Place = '1'
GROUP BY Event_id;

但我真的无法在第二个＆＃39;中添加SQL。和＆＃39;第三＆＃39;部分问题。

有人可以帮忙吗？

谢谢！

Answer 1

为什么不使用多个连接执行一个select语句，而不是使用子查询执行多个选择？

SELECT tb.event_id,
       tb1.money AS first,
       tb2.money AS second,
       tb3.money AS third
  FROM prize tb
       INNER JOIN prize tb1 ON tb1.event_id = tb.event_id AND tb1.place = 1
       INNER JOIN prize tb2 ON tb2.event_id = tb.event_id AND tb2.place = 2
       INNER JOIN prize tb3 ON tb3.event_id = tb.event_id AND tb3.place = 3
GROUP BY tb.event_id;

Answer 2

我会使用条件聚合来解决这个问题：

/my/logdir/Host1Server1.log
/my/logdir/Host1Server2.log
/my/logdir/Host2Server1.log
/my/logdir/Host2Server2.log

注意：如果有关系，那么这会增加所有地方的钱。

Answer 3

SELECT E.Event_ID, 
   (SELECT Money FROM PRIZE AS p1 WHERE Place = '1' AND p1.Event_ID = e.Event_ID) AS 'First',
   (SELECT Money FROM PRIZE AS p2 WHERE Place = '2' AND p2.Event_ID = e.Event_ID) AS 'Second',
   (SELECT Money FROM PRIZE AS p3 WHERE Place = '3' AND p3.Event_ID = e.Event_ID) AS 'Third'
FROM 
   (SELECT DISTINCT Event_ID
   FROM PRIZE) AS E

希望这有帮助

Answer 4

如果每个地方只有一个价格，并且每个Event_id这个查询应该适合您的目的。

Select Event_id
,FIRST=Max(CASE WHEN Place=1 THEN Money END)
,SECOND=Max(CASE WHEN Place=2 THEN Money END)
,THIRD=Max(CASE WHEN Place=3 THEN Money END)
from PRIZE
Group by Event_id

Answer 5

如果您只想要三列，那么使用条件聚合是最简单的数据透视方式：

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;

如果你想要一个动态解决方案，每个地方都有一个列，那么这个查询（改编自this question and answer）会这样做：

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'MAX(CASE WHEN Place = ''',
      Place,
      ''' THEN Money END) AS `',
      Place, '`'
    )
  ) INTO @sql
FROM  prize;

SET @sql = CONCAT('SELECT Event_id, ', @sql, ' 
                  FROM prize 
                  GROUP BY Event_id');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

这会将数字作为列名，但是如果你想要序数，你可以创建一个查找表并加入它。

Sample SQL Fiddle两种解决方案。

协助SQL子查询

5 个答案: