How to combine multiple records from a joined table - sql

Question

I'm out of my depth with this SQL query.
I have two tables A and B with shared data based on a serial number. In table A, there is a unique Serial Nr field, while in B, details relating to a particular serial number are linked vertically over multiple records by a common Group ID. The serial number entry occurs as one of those records in the MyData field. I want to concatenate all records that share the same "Group ID" to a single field in A. For example:
Table A
Serial Nr Name Part Nr
2950 Prod1 1234
2955 Prod2 2345
Table B
Group ID MyData Comments
1 2950 serial nr
1 2016-10 build month
2 2955 serial nr
2 2015-11 build month
and I want Table AxB
Serial Nr Name Part Nr Table B data
2950 Prod1 1234 serial nr, 2950, build month, 2016-10
2955 Prod2 2345 serial nr, 2955, build month, 2015-11
I don't actually want the shared Group ID, but need it as concatenation key.
I have tried to do this with STUFF, but to no avail. Any ideas?

Answer 1

I assume your "TableB" also has a "SerialNr" field (which you just did not model);
That is to say, your Table B actually looks like this:
Serial Nr Group ID MyData Comments
2950 1 2950 serial nr
2950 1 2016-10 build month
2955 2 2955 serial nr
2955 2 2015-11 build month
If so, the following query will aggregate the "Comments" and "MyData" columns into a single row per SerialNumber:
SELECT serialno ,STUFF((SELECT ', ' + Comments + ' - ' + MyData [text()]
FROM TableB
WHERE SerialNo = t.SerialNo
FOR XML PATH(''), TYPE).value('.','NVARCHAR(MAX)'),1,2,' ') AggregatedData
FROM TableB t
GROUP BY serialno
You could then join that query to your original TableA to obtain the result set you posted, ie:
select *
from TableA
join (SELECT serialno ,STUFF((SELECT ', ' + Comments + ' - ' + MyData [text()]
FROM TableB
WHERE SerialNo = t.SerialNo
FOR XML PATH(''), TYPE).value('.','NVARCHAR(MAX)'),1,2,' ') AggregatedData
FROM TableB t
GROUP BY serialno
) AggregatedTableB
on TableA.SerialNo = AggregatedTableB.SerialNo
UPDATED:
Ok - so based on the fact that your "TableB" doesn't have its own SerialNr row, and instead its buried within the table data.. You need to find a way to extract that row-level data into a column.
Here is a query that can do that:
select tableB.GroupId, MyData, Comments, SerialNo
from tableB
join
(select MyData as serialNo, groupId
from tableb
where Comments ='serial nr') TableBWithSerialNo on tableB.GroupId = TableBWithSerialNo.GroupId
Now that you have this query which adds the Serial No as a column, you can use it in place of just using TableB in the above query. Here's what it would look like:
SELECT SerialNo ,STUFF((SELECT ', ' + Comments + ' - ' + MyData [text()]
FROM
(select tableB.GroupId, MyData, Comments, SerialNo
from tableB
join
(select MyData as serialNo, groupId
from tableb
where Comments ='serial nr') TableBWithSerialNo on tableB.GroupId = TableBWithSerialNo.GroupId
) t1
WHERE t1.SerialNo = t2.SerialNo
FOR XML PATH(''), TYPE).value('.','NVARCHAR(MAX)'),1,2,' ') AggregatedData
FROM (select tableB.GroupId, MyData, Comments, SerialNo
from tableB
join
(select MyData as serialNo, groupId
from tableb
where Comments ='serial nr') TableBWithSerialNo on tableB.GroupId = TableBWithSerialNo.GroupId
) t2
GROUP BY SerialNo
Granted - this is one ugly query - but that's one ugly table you are working with ;-)
If anything, I'd recommend making the first query into a view, and then using that view in the second query - that way you aren't repeating so much code, ie;
create view TableBView as
select tableB.GroupId, MyData, Comments, SerialNo
from tableB
join
(select MyData as serialNo, groupId
from tableb
where Comments ='serial nr') TableBWithSerialNo on tableB.GroupId = TableBWithSerialNo.GroupId
go
SELECT SerialNo ,STUFF((SELECT ', ' + Comments + ' - ' + MyData [text()]
FROM
TableBView t1
WHERE t1.SerialNo = t2.SerialNo
FOR XML PATH(''), TYPE).value('.','NVARCHAR(MAX)'),1,2,' ') AggregatedData
FROM TableBView t2
GROUP BY SerialNo