How to write query using self join and group by? - sql

Question

I have sql server 2008 db table FILE_DETAILS in following format.
ID FileName Filesize_in_MB
--------------------------------
1 a.txt 5
2 b.txt 2
3 c.txt 2
3 d.txt 4
4 e.txt 6
4 f.txt 1
4 g.txt 2
5 h.txt 8
6 i.txt 7
now what i want to fetch is as bellow
ID FileName Filesize_in_MB
--------------------------------
1 a.txt 5
2 b.txt 2
3 c.txt;d.txt 6
4 e.txt;f.txt;g.txt 9
5 h.txt 8
6 i.txt 7
In above results what happens ID became unique key and FILENAME has get attached and separated by ; and also FILESIZE_IN_MB field in sum of group by ID
I tried with various combination like groupby + self join, also sub queries and all that
but i think i missing something.
is it possible to handle this in SQL query?
Thanks in advance

Answer 1

Try this:
SELECT ID,
STUFF(( SELECT ';' + [FileName]
FROM FILE_DETAILS
WHERE ID = f.ID FOR XML PATH('')), 1, 1, ''),
SUM(Filesize_in_MB)
FROM FILE_DETAILS f
GROUP BY ID
Here's some more information:
Concatenate many rows into a single text string?

Answer 2

You should be able to do this using a group by. Aggregating Filesize_IN_MB can be done using sum as aggregator. However, to aggregate FileName you may need to create an AGGREGATE in SQL SERVER 2008R2. This will allow you to use Concatenate as an aggregation function.
select Concatenate(FileName), sum(Filesize_IN_MB) FROM FILE_DETAILS group by ID
There is another way of aggregate concatenation which seems fairly simple but I haven't tried.