Combine Rows into a Column

Happened to find a way to combine rows into a column. I find it quite useful, and it comes in handy.

For illustration, suppose we have UserGroup & Users. We want to list the users belonging to each group.

UserGroup:

Users:

If we do normal joining of the 2 tables, it will look like:

If we combine the values on the rows into a column, it will look like:

Here is the query to do so:

-- Create temporary table to store UserGroup
SELECT GroupID = 1, UserGroup = 'Group 1' INTO #UserGroup
INSERT INTO #UserGroup VALUES ( 2, 'Group 2' )
INSERT INTO #UserGroup VALUES ( 3, 'Group 3' )

-- Create temporary table to store Users
SELECT UserID = 'Superman', GroupID = 1 INTO #Users
INSERT INTO #Users VALUES ( 'Luck', 2 )
INSERT INTO #Users VALUES ( 'Himura', 1 )
INSERT INTO #Users VALUES ( 'Selvi', 1 )
INSERT INTO #Users VALUES ( 'Smarty', 2 )
INSERT INTO #Users VALUES ( 'Lucky', 3 )

-- Normal Join
SELECT a.UserGroup, b.UserID
FROM #UserGroup a
LEFT JOIN #Users b
 ON b.GroupID = a.GroupID
ORDER BY a.UserGroup

-- Combine Rows into Column
SELECT UserGroup, Users = STUFF(( SELECT ', ' + UserID FROM #Users a
    WHERE a.GroupID = b.GroupID
    ORDER BY a.UserID
    FOR XML PATH('') )
   , 1, 2, '')
FROM #UserGroup b
ORDER BY UserGroup

-- This is the key query to combine rows into column
SELECT UserID + ', ' FROM #Users
WHERE GroupID = 1
FOR XML PATH('')

If you are concatenating a field which contains some HTML tag, it would be automatically encoded. To avoid that, consider using this query:

-- Combine Rows into Column
SELECT UserGroup, Users = STUFF(( SELECT ', ' + UserID FROM #Users a
    WHERE a.GroupID = b.GroupID
    ORDER BY a.UserID
    FOR XML PATH,TYPE).value('.[1]','nvarchar(max)')
   , 1, 2, '')
FROM #UserGroup b
ORDER BY UserGroup

Update: Looks like I posted something similar quite some time ago, but using different method: Selecting several rows into one row in SQL

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