sql：为什么在使用'GROUP CONCAT'+'GROUP BY'时查询重复值？

The Query:

SELECT MemberId, a.MemberName, GROUP_CONCAT(FruitName) FROM a LEFT JOIN b ON 
a.MemberName = b.MemberName GROUP BY a.MemberName

Table a

MemberID          MemberName              
--------------    ----------  
1                  Al                   
1                  Al       
3                  A2       

Table b

MemberName             FruitName
---------------        --------------
Al                     Apple
Al                     Mango
A2                     Cherry

Resulting Output from above query:

上述查询产生的结果:

MemberId    MemberName  GROUP_CONCAT(FruitName)
3           A2          Cherry
1           A1          Apple,Apple,Mango,Mango

The actual tables I am using have 10 columns apiece so just storing everything in one table is not a workaround. That said, how can I change the query to only return 'Apple,Mango' for MemberName?

我使用的实际表格各有10列,所以只将一切存储在一个表中不是一种解决方法。也就是说,如何才能将查询更改为仅返回“Apple,Mango”作为MemberName?

3 个解决方案

#1

Add the keyword DISTINCT to the grouped column:

将关键字DISTINCT添加到分组列:

GROUP_CONCAT(DISTINCT FruitName)

#2

try

GROUP_CONCAT(Distinct FruitName)

#3

SELECT  MemberId, a.MemberName, GROUP_CONCAT(DISTINCT FruitName)
FROM    a
LEFT JOIN
        b
ON      a.MemberName = b.MemberName
GROUP BY
        a.MemberName