Question

I need to find a way to add a Session column in a SELECT query. I’m using SQL Server 2005.

Here’s the initial example data:

ID    Name      VisitCounter    
1     TOM           1   
2     TOM           2   
3     TOM           3   
4     DICK          1       
5     DICK          2       
6     DICK          3       
7     DICK          4       
8     HARRY         1       
9     HARRY         2       
10    TOM           1   
11    TOM           2   
12    DICK          1       
13    DICK          2       

I need to write a query that will add a column called ‘Session’ and then increment everytime the name changes and the visitcounter = 1.

So the query should result in this:

ID    Name      VisitCounter    Session
1     TOM           1               1
2     TOM           2               1
3     TOM           3               1
4     DICK          1               2
5     DICK          2               2
6     DICK          3               2
7     DICK          4               2
8     HARRY         1               3
9     HARRY         2               3
10    TOM           1               4
11    TOM           2               4
12    DICK          1               5
13    DICK          2               5 and so on

Is this possible?

Answer 1

In your example data, the sessions do not overlap. If that is true in general, you could count the number of previously started sessions:

select  yt.ID
,       yt.Name
,       yt.VisitCounter
,       count(prev.ID) as Session
from    YourTable yt
join    YourTable prev
on      prev.ID <= yt.ID and
        prev.VisitCounter = 1
group by
        yt.ID
,       yt.Name
,       yt.VisitCounter
order by 
        yt.ID

Working example at SQL Fiddle.