将两行结果合并为一行MYSQL

Question

我有一个具有以下结构的表：

| pid | email | email_type |
| 1   | x     | 1          |
| 1   | y     | 2          |
| 1   | z     | 3          |
| 2   | ab    | 1          |
| 3   | cd    | 2          |

现在我想要pid 参数的结果，格式仅适用于email_type[1 & 2]：

案例pid=1

| pid | email_p | email_w |
| 1   | x       | y       |

案例pid=2

| 2   | ab      | NULL    |

案例pid=3

| 3   | NULL    | cd      |

这里email_p代表email_type=1&email_w代表email_type=2

我正在使用以下查询，除了 pid=2 的情况外，它工作正常。案例 I 和案例 III 已成功获取。请提供一些具有良好解释的解决方案（如果可能的话）。

SELECT `e`.`pid`, `e`.`email` AS `email_p`, `e1`.`email` AS `email_w` FROM `table1` AS `e` LEFT JOIN `table1` AS `e1` ON e.pid=e1.pid AND e1.email_type=2 WHERE (e.pid IN (1) AND e.email_type=1)

当e.pid = 2 失败并返回空结果集&请提供解决方案e.pid IN (1,2,3) 适用于所需格式。#MYSQL

Answer 1

试试这个

SELECT pid,
       MAX(CASE WHEN email_type=1 THEN email END ) as email_p ,
       MAX(CASE WHEN email_type=2 THEN email END ) as email_w 
FROM tableName
WHERE email_type IN (1,2)
GROUP BY pid

SQL Fiddle DEMO