Using functions in plsql

Question

Hello All:
My question is, Which is more efficient to use in Plsql:
IF v_DestFile IS NULL THEN
v_DestFile := in_DestFile ;
END IF;
OR
v_DestFile := NVL(v_DestFile , in_DestFile);
Using the second one requires a call to a function..
What are your thoughts.
Thanks
Leonard

Answer 1

The following test run on Windows XP with an Athlon 3400 shows that NVL function take more time to execute. However to see the difference you have to run this code many many times (if you run this this code 1 million of times within a SQL query or within PL/SQL, you will likely get other performance problems ...):
SQL> set timing on
SQL>
SQL> select * from v$version;
BANNER                                                                         
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod               
PL/SQL Release 10.2.0.1.0 - Production                                         
CORE     10.2.0.1.0     Production                                                     
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production                        
NLSRTL Version 10.2.0.1.0 - Production                                         
Elapsed: 00:00:00.00
SQL>
SQL> declare
  2  vdf varchar2(10) := null;
  3  vidf varchar2(10) := 'ok';
  4  begin
  5   for i in 1..100000000
  6   loop
  7    if vdf is null then
  8    vdf := vidf;
  9    end if;
10   end loop;
11  end;
12  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.57
SQL> show errors
No errors.
SQL>
SQL>
SQL> declare
  2  vdf varchar2(10) := null;
  3  vidf varchar2(10) := 'ok';
  4  begin
  5   for i in 1..100000000
  6   loop
  7    vdf := nvl(vdf, vidf);
  8   end loop;
  9  end;
10  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:21.71
SQL> show errors
No errors.
SQL>
SQL>
SQL> declare
  2  vdf varchar2(10) := 'ok';
  3  vidf varchar2(10) := 'ok';
  4  begin
  5   for i in 1..100000000
  6   loop
  7    if vdf is null then
  8    vdf := vidf;
  9    end if;
10   end loop;
11  end;
12  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.61
SQL> show errors
No errors.
SQL>
SQL>
SQL> declare
  2  vdf varchar2(10) := 'ok';
  3  vidf varchar2(10) := 'ok';
  4  begin
  5   for i in 1..100000000
  6   loop
  7    vdf := nvl(vdf, vidf);
  8   end loop;
  9  end;
10  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:21.76
SQL> show errors
No errors.
SQL> exit
[pre]
Message was edited by:
        Pierre Forstmann
Message was edited by:
        Pierre Forstmann