Oracle Upsert using merge

gistfile1.txt

MERGE INTO target_name T USING
( select 1 from dual) S ON
( clause_that_finds_record inside T )
WHEN MATCHED THEN UPDATE 
  SET update_what_you_want_in_T 
WHEN NOT MATCHED THEN
  INSERT(
    stuff_in_t 
  ) VALUES(  ...values... );