SQL & PL/SQL

I have tables S and T in Oracle 10g database, and i often join those tables like following way:

WITH s AS
 (SELECT 1 Id FROM Dual),
t AS
 (SELECT 1 Id1, NULL Id2
  FROM Dual
  UNION ALL
  SELECT 1, 1
  FROM Dual
  UNION ALL
  SELECT NULL, 1 FROM Dual)
SELECT s.Id, t.* FROM t, s WHERE s.Id = Coalesce(t.Id1, t.Id2);
/*
 1 1 
 1 1 1
 1   1
*/

Is there any index i could create that would make such join faster to perform?