create table tbl_temp_A as select rownum as num, t.a as col_A from A t;

create table tbl_temp_B as select rownum as num, t.b as col_B from B t;

create table tbl_C 
(
   a   data_type   -- A表的a字段
   b   data_type   -- B表的b字段
)
insert into tbl_C 
(
  a,
  b
)
   select t1.col_A,
          t2.col_B
     from tbl_temp_A  t1
   full join tbl_temp_B t2
     on t1.num = t2.num;

drop table tbl_temp_A;
drop table tbl_temp_B;