Functions slowing down performance question

Question

Hey there.
I've got a query that really slogs. This query calls quite a few functions and there's no question that some of the work that needs to be done, simply takes time.
However, someone has adamantly told me that using functions slow down the query compared to the same code in the base SQL.
I find this hard to believe that the exact same code - whether well written or not - would be much faster in the base view than having a view call the functions.
Is this correct that functions kill performance?
Thanks for any advice.
Russ

Answer 1

There is the performance impact of context switching between SQL and PL/SQL engines. Pure SQL is always faster.
SQL> create or replace function f (n number) return number as
  2  begin
  3    return n + 1;
  4  end;
  5  /
Function created.
SQL> set timing on
SQL> select sum(f(level)) from dual
  2  connect by level <= 1000000;
SUM(F(LEVEL))
   5.0000E+11
Elapsed: 00:00:07.06
SQL> select sum(level + 1) from dual
  2  connect by level <= 1000000;
SUM(LEVEL+1)
  5.0000E+11
Elapsed: 00:00:01.09