MySql：从同一个表的三个不同列中提取不同的条目

Question

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clients表，其中包含clientName和client_id字段。

如何在表格交易的三列中的任何一列中创建其ID为其的名称的字符串数组。

Answer 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

说明：

从一个表中获取客户端：

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

联盟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)

现在要获得一个Comma-Seperated-String，要么使用GROUP_CONCAT来执行此客户端（php）或让MySQL服务器执行此操作：

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