Merge in oracle

Question

I have a table A and Table B. I want to use a merge statement for following
1) If Not matched then update values in Table B from table A.
2) If not matched then insert values from table A to Table B
3) If value is present in Table B and not in Table A it should delete the value from Table B as well.
Can we achive this using merge statement.? If yes how?. point no 1 and 2 can be but I want to know how can it use for point 3.
Thanks for any help.

Answer 1

Solomon Yakobson wrote:
3) & 1) are conflicting.Oops,
I misread 3). You could:
create table tbl1
  as
    select  level id,
            chr(ascii('A') + level - 1) val
      from  dual
      connect by level <= 10
create table tbl2
  as
    select  level + 5 id,
            chr(ascii('A') + level + 4) val
      from  dual
      connect by level <= 10
select  *
  from  tbl1
select  *
  from  tbl2
SQL> select  *
  2    from  tbl1
  3  /
        ID V
         1 A
         2 B
         3 C
         4 D
         5 E
         6 F
         7 G
         8 H
         9 I
        10 J
10 rows selected.
SQL> select  *
  2    from  tbl2
  3  /
        ID V
         6 F
         7 G
         8 H
         9 I
        10 J
        11 K
        12 L
        13 M
        14 N
        15 O
10 rows selected.
merge
  into tbl1 t1
  using (
          select  id,
                  val,
                  1 weight
            from  tbl2
         union all
          select  id,
                  val,
                  2 weight
            from  tbl1
            where id not in (
                             select  id
                               from  tbl2
        ) t2
  on (
      t1.id = t2.id
  when not matched
    then
      insert
        values(
               t2.id,
               t2.val
  when matched
    then
      update
        set val = t2.val
        delete where t2.weight = 2
SQL> select  *
  2    from  tbl1
  3    order by id
  4  /
        ID V
         6 F
         7 G
         8 H
         9 I
        10 J
        11 K
        12 L
        13 M
        14 N
        15 O
10 rows selected.
SQL> SY.