SQL：如果有多个唯一键，则对应的值应为空

我有一张这样的桌子：

email_1          | name_1   | email_2             | name_2 
+----------------+----------+---------------------+----------
sandy@name.com   | Sandy    | sandy@name.com      | Sandy 
sandy@name.com   | Sandy    | sandy@name.com      | Pat 
chris@name.com   | Chris    |                     | 
george@name.com  | George   | george@name.com     | Shelly 
george@name.com  | George   | george@name.com     | George 
hank@name.com    | Hank     | hank@name.com       | Barbara
hank@name.com    | Hank     | hank@name.com       | Hank
mikey@name.com   | Mikey    |                     | 

同一个电子邮件地址有多个名称。对于具有多个名称的电子邮件地址，我想创建一个表，列出不同的电子邮件和名称的

Null

。仅附加一个名称的电子邮件将保留该名称

结果表：

email            | name   
+----------------+----------+
sandy@name.com   |          | 
chris@name.com   | Chris    |                      
george@name.com  |          |
hank@name.com    |          |
mikey@name.com   | Mikey    |

---

我将如何编写查询来执行此操作？

您要取消PIVOT并聚合：

select email,
       (case when min(name) = max(name) then min(name) end) as name
from ((select email_1 as email, name_1 as name from t
      ) union all
      (select email_2 as email, name_2 as name from t
      )
     ) e
group by email;

---

要取消打印并聚合：

select email,
       (case when min(name) = max(name) then min(name) end) as name
from ((select email_1 as email, name_1 as name from t
      ) union all
      (select email_2 as email, name_2 as name from t
      )
     ) e
group by email;

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用你正在使用的数据库标记你的问题。用你正在使用的数据库标记你的问题。