Group_concat 添加了列答案

【问题标题】：Group_concat with added columnsGroup_concat 添加了列
【发布时间】：2017-07-31 16:56:48
【问题描述】：

我得到了一个运行良好的查询：

SELECT Course, Period, Room, Location, TeacherId, GROUP_CONCAT(StudentId) as Students 
FROM cursosv2 
GROUP BY Course, Period, Room, Location, TeacherID;

我想要的（可能太基本了）是在生成的查询中拥有一个新列，例如 NEW COLUMN A，其连接值为 period+room+'final'。但我不断收到异常。不知道真正的原因。

我在尝试什么...

SELECT Course, Period, Room, Period+' '+Room+' Final' as test, Location, TeacherId, GROUP_CONCAT(StudentId) as Students 
FROM cursosv2 
GROUP BY Course, Period, Room, Location, TeacherID;

谢谢。

【问题讨论】：

标签： mysql group-by group-concat

【解决方案1】：

您还应该使用 concat 进行字符串连接（不是 + ）并添加到 group by

 SELECT Course, Period, Room, concat( Period,' ',Room,' Final') as test, Location, TeacherId, GROUP_CONCAT(StudentId) as Students 

 FROM cursosv2 
 GROUP BY Course, Period, test, Room, Location, TeacherID;

【讨论】：

【解决方案2】：

使用concat 代替+ 连接。并将test 添加到group by 子句中：

SELECT Course, Period, Room, concat(Period,' ',Room,' Final') as test, 
       Location, TeacherId, GROUP_CONCAT(StudentId) as Students 
FROM cursosv2 
GROUP BY Course, Period, Room, test, Location, TeacherID;

【讨论】：

【解决方案3】：

您可以使用 CONCAT_WS 来实现。

(' ', Column1, column2) AS column_name

SELECT Course, Period, Room, concat_ws(' ', Room, Period) AS roomperiod, Location, TeacherId, GROUP_CONCAT(StudentId) as Students FROM cursosv2 GROUP BY Course, Period, Room, Location, TeacherID;

https://dev.mysql.com/doc/refman/5.5/en/string-functions.html#function_concat-ws

【讨论】：

分隔符应该是空格。