That is what the query I posted will show you.
Here is another way to get the same results, but it has a bit more complicated execution plan.
select StudentID, Case when COUNT(*) > 1 then 1 else 0 end as Marker
from #MathScience
where StudentID in (select StudentID from #MathScience where SubjectChoice = 'Math')
group by StudentID
If there is something missing then you will need to post YOUR ddl, sample data and desired output. The stuff I am working with is because you didn't provide so I had to make some up.
_______________________________________________________________
Need help? Help us help you.
Read the article at http://www.sqlservercentral.com/articles/Best+Practices/61537/ for best practices on asking questions.
Need to split a string? Try Jeff Modens splitter http://www.sqlservercentral.com/articles/Tally+Table/72993/.
Cross Tabs and Pivots, Part 1 – Converting Rows to Columns - http://www.sqlservercentral.com/articles/T-SQL/63681/
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs - http://www.sqlservercentral.com/articles/Crosstab/65048/
Understanding and Using APPLY (Part 1) - http://www.sqlservercentral.com/articles/APPLY/69953/
Understanding and Using APPLY (Part 2) - http://www.sqlservercentral.com/articles/APPLY/69954/