---Let Oracle go first
SELECT /*+ CHOOSE */ 
      A.order_id
FROM TABLE_A A, 
     TABLE_B B 
WHERE A.order_id = B.order_id;

---Repeat above with /*+ USE_HASH(a b) */

SELECT A.order_id from TABLE_A A 
   WHERE EXISTS (SELECT 1 FROM TABLE_B B 
                          WHERE A.order_id = 
                                B.order_id);

SELECT   A.order_id from TABLE_A A 
   WHERE A.order_id IN 
    (SELECT B.order_id from TABLE_B B);

SELECT A.order_id from TABLE_A A 
  WHERE A.order_id NOT IN
((SELECT order_id from TABLE_A where order_id is not null)
minus
 (SELECT order_id from TABLE_B)); --can't be null if 
                                 --Oracle could use a FFS
                                 -- on the index

create table test_0077 (col_1 number, col_2 varchar2(10));

create table test_0078 (col_1 number, col_2 varchar2(10));

insert into test_0077  select level,'AAAAA' from dual connect by level <=20;

insert into test_0078 select level*2,'BBBBB' from dual connect by level <=10;

commit;

update (select t1.col_1,t1.col_2 old_c2 ,t2.col_2 new_c2
        from   test_0077 t1, test_0078 t2
        where  t1.col_1 = t2.col_1)
set     old_c2 = new_c2;

ERROR at line 4:
ORA-01779: cannot modify a column which maps to a non key-preserved table

update (select /*+ bypass_ujvc */ t1.col_1,t1.col_2 old_c2 ,t2.col_2 new_c2
        from   test_0077 t1, test_0078 t2
        where  t1.col_1 = t2.col_1)
set     old_c2 = new_c2;

10 rows updated.

select * from test_0077;

     COL_1 COL_2
---------- ----------
         1 AAAAA
         2 BBBBB
         3 AAAAA
         4 BBBBB
         5 AAAAA
         6 BBBBB
         7 AAAAA
         8 BBBBB
         9 AAAAA
        10 BBBBB
        11 AAAAA

     COL_1 COL_2
---------- ----------
        12 BBBBB
        13 AAAAA
        14 BBBBB
        15 AAAAA
        16 BBBBB
        17 AAAAA
        18 BBBBB
        19 AAAAA
        20 BBBBB

20 rows selected.

SQL> merge into test_0077 t7 using test_0078 t8 on (t8.col_1=t7.col_1)
  2  when matched then update set col_2=t8.col_2
  3  /

10 rows merged.

SQL> select * from test_0077;
     COL_1 COL_2
---------- ----------
         1 AAAAA
         2 BBBBB
         3 AAAAA
         4 BBBBB
         5 AAAAA
         6 BBBBB
         7 AAAAA
         8 BBBBB
         9 AAAAA
        10 BBBBB
        11 AAAAA
        12 BBBBB
        13 AAAAA
        14 BBBBB
        15 AAAAA
        16 BBBBB
        17 AAAAA
        18 BBBBB
        19 AAAAA
        20 BBBBB

20 rows selected.