Do multiple "case" lines run against each line or is each run against the table ?

[KaronW]

I have informix 9.40.FC7. I have a 31 million line table that I extract information from. It takes up to 7 days now to finish. I don't know if it runs the 4 "case" lines against each row or if it is running 1 "case" against the 31 million rows and then moves to the next "case". Any ideas? I'd appreciate any assistance! Thanks!

set isolation to dirty read;

select f.patkey,f.invno,f.orderno,f.dx_orderno
from findiag f
into temp temp1 with no log;

select t.patkey,t.invno,
    case
      when t.orderno = 1 then p.dxcode else " " end diag1,
    case
      when t.orderno = 2 then p.dxcode else " " end diag2,
    case
      when t.orderno = 3 then p.dxcode else " " end diag3,
    case
      when t.orderno = 4 then p.dxcode else " " end diag4
from temp1 t,patdiag p
where t.patkey = p.patkey
  and t.dx_orderno = p.order_no
  and p.active = 'Y'
into temp temp2 with no log;

unload to 'trandiag1.txt'
select * from temp2;    

unload to 'trandiag.txt'
select t.patkey,t.invno,MAX(diag1) as d1,
        MAX(diag2) as d2,
        MAX(diag3) as d3,
        MAX(diag4) as d4
from temp2 t
group by 1,2;