Group_concat与添加的列

Question

我有一个查询，可以正常工作：

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

我想要的（可能太基础了）是在结果查询中有一个新列，例如NEW COLUMN A，其连接值是period + room +'final'。 但是我一直在例外。 不知道真正的原因。

我在想什么...

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。

Answer 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;

Answer 2

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

Answer 3

使用concat串联而不是+ 。 并将test添加到group by子句：

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;