Problem in getting Sum

Question

I have this data:

name    qty     date                    flag  
---------------------------------------------    
abc     255     11/10/1986 12:00:00 AM  IN
abc     300     11/10/2010 12:00:00 AM  IN
abc     12      11/10/2012 12:00:00 AM  OUT
abc     13      11/9/2010 12:00:00 AM   OUT
NULL    NULL    NULL                    NULL

I want to get sum of qty at that specific row:

• If flag is "in", then it will add to the sum
• if flag is "out", then it will subtract from the sum

Answer 1

SELECT SUM(case flag when 'IN' then qty else -qty end)
from table
WHERE ..... Your conditions here ...