以列形式查询行（MySQL）

我的表格结构：

cust_id | action   | action_count
--------+----------+-------------
1       | Approved | 15
2       | Approved | 25
1       | Rejected | 6
2       | Pending  | 20
2       | Rejected | 7

我必须以如下方式获得查询结果：

cust_id | Approved | Pending | Rejected
--------+----------+---------+---------
1       | 15       | 0       | 6
2       | 25       | 20      | 7

请尝试此查询

select 
   cust_id, 
   max(if(action='Approved', action_count, 0)) as Approved,
   max(if(action='Rejected', action_count, 0)) as Rejected,
   max(if(action='Pending', action_count, 0)) as Pending
from 
   tbl
group by 
   cust_id

---

如果

操作

的数量已知，这里有一个静态查询

SELECT  cust_id,
        COALESCE(MAX(CASE WHEN action = 'Approved' THEN action_Count END), 0) Approved,
        COALESCE(MAX(CASE WHEN action = 'Pending ' THEN action_Count END), 0) Pending ,
        COALESCE(MAX(CASE WHEN action = 'Rejected' THEN action_Count END), 0) Rejected 
FROM    TableName
GROUP   BY cust_id

但是如果

action

的值的数目未知，则更倾向于使用动态sql

SELECT  GROUP_CONCAT(DISTINCT
        CONCAT('COALESCE(MAX(CASE WHEN action = ''',
               action,
               ''' THEN action_Count END), 0) AS ',
               CONCAT('`', action, '`')
               )) INTO @sql
FROM TableName;

SET @sql = CONCAT('SELECT   cust_id, ', @sql, ' 
                    FROM    TableName
                    GROUP   BY cust_id');

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

---

+1而且@Meherzad打得很好-比我快了10秒：）谢谢@Meherzad，你的提问帮助了我。我用SUM（）而不是max（）解决了这个问题。您可以根据查询的需要使用任何聚合函数。@Meherzad，我想按批准列的降序对列进行排序。如何做到这一点。请帮帮我。。

SELECT  GROUP_CONCAT(DISTINCT
        CONCAT('COALESCE(MAX(CASE WHEN action = ''',
               action,
               ''' THEN action_Count END), 0) AS ',
               CONCAT('`', action, '`')
               )) INTO @sql
FROM TableName;

SET @sql = CONCAT('SELECT   cust_id, ', @sql, ' 
                    FROM    TableName
                    GROUP   BY cust_id');

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