MySql：从同一张表的三个不同列中提取不同的条目

Posted 2023-02-24

【中文标题】MySql：从同一张表的三个不同列中提取不同的条目

【英文标题】：MySql: extracting distinct entries from three different columns of same table

【发布时间】：2011-11-05 19:30:04

【问题描述】：

我有一个名为deals 的表，其中存储了client_id1、client_id2、client_id3。

这些 id 对应于具有 clientName 和 client_id 字段的 clients 表。

如何创建一个名称的字符串数组，其 id 存在于表交易的三列中的任何一列中。

【问题讨论】：

你或许应该考虑规范化你的数据。

【参考方案1】：

SELECT GROUP_CONCAT(Client) FROM (
 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id1 = clients.client_id
UNION ALL
 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id2 = clients.client_id
UNION ALL
 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id3 = clients.client_id)
GROUP BY Client

解释：

从一张表中获取客户端：

 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id1 = clients.client_id

联合也会从其他表中获取它们

 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id1 = clients.client_id
UNION ALL
 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id2 = clients.client_id
UNION ALL
 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id3 = clients.client_id)

现在要获取逗号分隔字符串，要么执行此客户端 (php)，要么让 mysql 服务器执行此操作，使用 GROUP_CONCAT：

SELECT GROUP_CONCAT(Client) FROM (
 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id1 = clients.client_id
UNION ALL
 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id2 = clients.client_id
UNION ALL
 SELECT clientName as Client 
 FROM deals JOIN clients
 ON deals.client_id3 = clients.client_id)
GROUP BY Client