Используйте условное insert all
как здесь:
create table a(x, y, z) as (select 0, 0, 0 from dual);
create table b(x, y, z) as (select 0, 0, 0 from dual);
create table c(x, y, z) as (select 0, 0, 0 from dual);
create table src(x, y, z) as (
select 1, 1, 1 from dual union all
select 2, 2, 2 from dual union all
select 3, 3, 3 from dual );
insert all
when x = 1 then into a (x, y, z) values (x, y, z)
when x = 2 then into b (x, y, z) values (x, y, z)
when x = 3 then into c (x, y, z) values (x, y, z)
select * from src