Is there any performance difference in the order of columns referencing index?

Question

I wish to find out if there is any performance difference or efficiency in specifying those columns referencing index(es) first in the WHERE clause of SQL statements. That is, whether the order of columns referencing the index is important???.
E.g. id is the column that is indexed
SELECT * FROM a where a.id='1' and a.name='John';
SELECT * FROM a where a.name='John' and a.id='1';
Is there any differences in terms of efficiency of the 2 statements??
Please advise. Thanks.

Answer 1

There is no difference between the two statements under either the RBO or the CBO.
sql>create table a as select * from all_objects;
Table created.
sql>create index a_index on a(object_id);
Index created.
sql>analyze table a compute statistics;
Table analyzed.
sql>select count(*)
  2    from a
  3   where object_id = 1
  4     and object_name = 'x';
COUNT(*)
        0
1 row selected.
Execution Plan
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=1 Card=1 Bytes=29)
   1    0   SORT (AGGREGATE)
   2    1     TABLE ACCESS (BY INDEX ROWID) OF 'A' (Cost=1 Card=1 Bytes=29)
   3    2       INDEX (RANGE SCAN) OF 'A_INDEX' (NON-UNIQUE) (Cost=1 Card=1)
sql>select count(*)
  2    from a
  3   where object_name = 'x'   
  4     and object_id = 1;
COUNT(*)
        0
1 row selected.
Execution Plan
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=1 Card=1 Bytes=29)
   1    0   SORT (AGGREGATE)
   2    1     TABLE ACCESS (BY INDEX ROWID) OF 'A' (Cost=1 Card=1 Bytes=29)
   3    2       INDEX (RANGE SCAN) OF 'A_INDEX' (NON-UNIQUE) (Cost=1 Card=1)