Hello all -

I have another SELECT problem I have not encountered before. I have this query which seems to work OK.

SELECT a.system,
      a.subsystem, 
      COUNT(a.system) as numprojects, 
      SUM(total_cost) as Total_Cost
  FROM systems a
  inner join rtp_projects b on a.system = b.system and a.subsystem = b.subsystem  
  where b.Basecase = 1
  group by a.system, a.subsystem
  order by a.system, a.subsystem

Now I need to add another column that shows the sum of the Total_cost of the projects where Category = 'Capacity', something like this

SELECT a.system,
      a.subsystem, 
      COUNT(a.system) as numprojects, 
      SUM(total_cost) as Total_Cost,
      SUM(Total_cost where Category = 'Capacity')
  FROM systems a
  inner join rtp_projects b on a.system = b.system and a.subsystem = b.subsystem  
  where b.Basecase = 1
  group by a.system, a.subsystem
  order by a.system, a.subsystem

but I can't figure out the syntax for this additional column. Can someone help?
Thanks