Number of working Days (Mon-Fri) between two dates?

[abhaysk]

How about this one which will not read any rows..jus a calculation and i suppose will be fastest !!

Select 
  Dayz 
       -
  Nvl(Floor(Round((Dayz+Add_To_Dayz)/7,2)) * 2, 0)
  Week_Days
From
  (
  Select 
    Trunc(End_Date) 
         - 
    Trunc(Start_Date) 
         - 
    Decode(Substr(To_Char(Start_Date, 'DAY'), 1, 3), 'SUN', 1,
                                                     'SAT', 2,
                                                            0
          ) 
         -
    Decode(Substr(To_Char(End_Date, 'DAY'), 1, 3), 'SUN', 2,
                                                   'SAT', 1,
                                                          0
          ) 
       +
    1
    Dayz, 
    Decode(Substr(To_Char(Start_Date, 'DAY'), 1, 3), 'MON', 1,
                                                     'TUE', 2,
                                                     'WED', 3,
                                                     'THU', 4,
                                                     'FRI', 5,
                                                            0
          ) Add_To_Dayz
  From
  Dual
  )
;

PS : I have tested for few cases, not thoroughly tested...but seems ok to me.

Abhay.