insert into Table1 (column1, column2, column4, column3)
select column1, column2, column3
from Table2
union
select column3
from Table3

select column1, column2, column3
from Table2
union all
select column3, null, null
from Table3

insert into Table1 (column1, column2, column4, column3)
    select t2.column1, t2.column2, t2.column3, t1.column3
    from Table2 t2 cross join
         Table3 t3;