Function for Performance

Question

Hi,
Does a function increase performance instead of a nested decode/case while handling huge data?
example:
select decode('6','1','0',decode('6','2','3',decode('6','4','5','6'))) from dual
select get_code('6') from dual;
get_code(m_code)
is return varchar2
begin
if m_code = '1' then return '0'
elsif m_code = '2' then return '3'
elsif m_code ='4' then return '5'
else return '6'
end;

Answer 1

No. PL inside SQL is never fast. Check this out.
SQL> create or replace function my_fn(pInput1 integer, pInput2 integer) return integer
  2  as
  3  begin
  4     if pInput1>pInput2
  5     then
  6             return 1;
  7     else
  8             return 0;
  9     end if;
10  end;
11  /
Function created.
SQL> create table t
  2  as
  3  select dbms_random.value(1,9999) no1, dbms_random.value(1,9999) no2
  4    from dual
  5  connect by level <= 100000
  6  /
Table created.
SQL> exec dbms_stats.gather_table_stats(user,'T')
PL/SQL procedure successfully completed.
SQL> set autotrace traceonly
SQL> set timing on
SQL>
SQL> select no1,
  2         no2,
  3         case when no1>no2 then 1 else 0 end val
  4    from t
  5  /
100000 rows selected.
*Elapsed: 00:00:46.03*
Execution Plan
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=159 Card=100000 By
          tes=4300000)
   1    0   TABLE ACCESS (FULL) OF 'T' (TABLE) (Cost=159 Card=100000 B
          ytes=4300000)
Statistics
          *1  recursive calls*
          0  db block gets
       7355  consistent gets
          0  physical reads
          0  redo size
    5830943  bytes sent via SQL*Net to client
      73826  bytes received via SQL*Net from client
       6668  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
     100000  rows processed
SQL> select no1,
  2         no2,
  3         my_fn(no1,no2)
  4    from t
  5  /
100000 rows selected.
*Elapsed: 00:00:49.04*
Execution Plan
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=159 Card=100000 By
          tes=4300000)
   1    0   TABLE ACCESS (FULL) OF 'T' (TABLE) (Cost=159 Card=100000 B
          ytes=4300000)
Statistics
         *18  recursive calls*
          0  db block gets
       7374  consistent gets
          0  physical reads
          0  redo size
    5830954  bytes sent via SQL*Net to client
      73826  bytes received via SQL*Net from client
       6668  SQL*Net roundtrips to/from client
          5  sorts (memory)
          0  sorts (disk)
     100000  rows processedThanks,
Karthick.