Need to concatenate results of a subquery in a select statement - mysql

Question

I have three tables
Table1: Users
Columns: User_ID (int), FirstName, LastName....
Values
1 Jane Doe
2 John Doe
3 Mike Smith
Table2: User_Groups
Columns: User_ID (int), Group_ID(int)
Values:
Row1: 1 2
Row2: 1 3
Row3: 2 1
Row4: 2 3
Row5: 3 1
Table3: Groups
Columns: Group_ID (int), GroupName(varchar)
Values
Row1: 1 Admin
Row2: 2 Power User
Row3: 3 Developer
I would like to create a query that can return the results in the following way:
**RESULT
UserID GroupNames
Row1: 1 Power User, Developer
Row2: 2 Admin, Developer
Row3: 3 Admin
In SQL Server - I was able to achieve it using something like this:
SELECT User_ID,
SUBSTRING(
replace(
replace(
(SELECT Groups.GroupName
FROM User_Groups, Groups
where groups.Group_ID =
User_Groups.Group_ID AND
User_Groups.User_ID =Users.User_ID
FOR XML PATH('') )
,'<GROUPNAME>',', ')
,'</GROUPNAME>',''),3,2000) as UserGroups
FROM User_Groups LEFT JOIN Groups ON
User_Groups.Group_ID=Groups.Group_ID
ORDER BY User_ID ASC
I wanted to do get a similar final result in MySQL (tried GROUP_CONCAT etc) but unsuccessful.. how can I get similar **RESULT in MySQL. Please note the tables exist already and I cant change them.
Any help will be greatly appreciated

Answer 1

This works:
SELECT
t1.User_ID AS UserID,
(
SELECT
GROUP_CONCAT(t2.GroupName)
FROM
Groups t2
WHERE
t2.Group_ID IN(
SELECT
t3.Group_ID
FROM
User_Groups t3
WHERE
t3.iUser_ID = t1.User_ID
)
) AS GroupNames
FROM
Users t1
And this look like better idea, since you don't want to have user names, so that's no need to involve Users table:
SELECT
User_ID,
GROUP_CONCAT(GroupName) AS GroupNames
FROM
(
SELECT
t2.User_ID AS User_ID,
t3.GroupName AS GroupName
FROM
User_Groups t2
LEFT JOIN
Groups t3 ON (t3.Group_ID = t2.Group_ID)
) tmp
GROUP BY
User_ID