GROUP BY to combine/concat a column [duplicate]

问题

This question already has answers here:

Simulating group_concat MySQL function in Microsoft SQL Server 2005? (10 answers)

Concatenate one field after GROUP BY (1 answer)

Closed 5 years ago.

I have a table as follow:

ID  User  Activity  PageURL  
 1  Me    act1      ab     
 2  Me    act1      cd     
 3  You   act2      xy     
 4  You   act2      st

I want to group by User and Activity such that I end up with something like:

User  Activity  PageURL  
Me    act1      ab, cd     
You   act2      xy, st

As you can see, the column PageURL is combined together separated by a comma based on the group by.

Would really appreciate any pointers and advice.

回答1:

SELECT
     [User], Activity,
     STUFF(
         (SELECT DISTINCT ',' + PageURL
          FROM TableName
          WHERE [User] = a.[User] AND Activity = a.Activity
          FOR XML PATH (''))
          , 1, 1, '')  AS URLList
FROM TableName AS a
GROUP BY [User], Activity

• SQLFiddle Demo

回答2:

A good question. Should tell you it took some time to crack this one. Here is my result.

DECLARE @TABLE TABLE
(  
ID INT,  
USERS VARCHAR(10),  
ACTIVITY VARCHAR(10),  
PAGEURL VARCHAR(10)  
)

INSERT INTO @TABLE  
VALUES  (1, 'Me', 'act1', 'ab'),
        (2, 'Me', 'act1', 'cd'),
        (3, 'You', 'act2', 'xy'),
        (4, 'You', 'act2', 'st')


SELECT T1.USERS, T1.ACTIVITY,   
        STUFF(  
        (  
        SELECT ',' + T2.PAGEURL  
        FROM @TABLE T2  
        WHERE T1.USERS = T2.USERS  
        FOR XML PATH ('')  
        ),1,1,'')  
FROM @TABLE T1  
GROUP BY T1.USERS, T1.ACTIVITY

来源：https://stackoverflow.com/questions/15154644/group-by-to-combine-concat-a-column