Performance issue: View query is calculating a column value before filterin

Question

Hi,
I have a view like this.(My view is more complex than this..I just tried to imitate the situation )
Select emp_id, emp_name, calculate_salary(emp_id) salary
  From employees
Where nvl(department, '@@##$$') = nvl(get_global.department, '@@##$$')When I execute the below query
select emp_name from my_view where salary=10000 by setting a value to get_globals.department I found that it first calls the calculate_salary instead of applying the filter for departments. By somehow the cost base analyzer thinks that calling the function is cheaper than applying the filter. I wonder whether there is way to direct the cba and say to first apply the filters before calculating column values.
Any suggestions ?
Thanks

Answer 1

I don't think it's possible.
Before a WHERE clause can be applied the data has to be collected for the row so Oracle, I would imagine, isn't going to differentiate between what is a database column and a function, fetch just the columns, do the filtering and then go back to calculate the rest of the columns; it's just going to get all the columns, including the calculated ones, and then apply the filters.
The only option would be to do...
select emp_id, emp_name, calculate_salary(emp_id) salary
from (select emp_id, emp_name
      from employees
      where nvl(deparment, '@@##$$') = nvl(get_global.department, '@@##$$')
      )as your view