Rolling Multiple Rows into a Single Row Based on Matching Data in SQL Server

I have a table in SQL Server with the following layout and some sample data:

| ReferenceNumber | TagID |
+-----------------+-------+
| 114942          |   1   |
| 114942          |   2   |
| 114942          |   3   |
| 114942          |   4   |
| 123456          |  10   |

Is it possible to consolidate like ReferenceNumber rows into a single row, so:

| ReferenceNumber | TagID   |
+-----------------+---------+
| 114942          | 1,2,3,4 |
| 123456          | 10      |

I’ve tried:

select 
    ReferenceNumber,
    stuff((select '; ' + TagID from RefTagTable
           for xml path('')), 1, 1,'')[Tags]
from 
    RefTagTable
order by 
    ReferenceNumber

which outputs:

| ReferenceNumber | Tags       |
+-----------------+------------+
| 114942          | 1,2,3,4,10 |
| 123456          | 1,2,3,4,10 |

Any help would be greatly appreciated. Thanks

Answer

Assuming this is for small (ish) amount of data, you can correlate the subquery. It nests (so the query can be thought of as running once per row in the outer query. The optimiser normally optimises better than that but depends a bit on volumes as to whether it works for you better than other approaches.

DROP TABLE #tags
GO

CREATE TABLE #tags (ReferenceNumber varchar(10), TagId varchar(20)) 
GO

INSERT INTO #tags (ReferenceNumber , TagId ) 
SELECT 114942, 1
UNION SELECT 114942, 2
UNION SELECT 114942, 3
UNION SELECT 114942, 4
UNION SELECT 123456, 1
GO

SELECT ReferenceNumber,
       stuff((select '; ' + TagID from #Tags AS CorrTagTable WHERE CorrTagTable.ReferenceNumber = Reftagtable.ReferenceNumber
for xml path('')), 1, 1,'')[Tags]
from #tags AS RefTagTable
order by ReferenceNumber

GO 

Produces:

ReferenceNumber Tags
114942          1; 2; 3; 4
114942          1; 2; 3; 4
114942          1; 2; 3; 4
114942          1; 2; 3; 4
123456          1