create trigger tr_a
on a
for insert
as
begin
declare @x1,@x2.....@xm
set @x1=(select x from a where ..)
..................
insert b(....) values(x1....xm)
declare @x1,@x2.....@xn
set @x1=(select x from a where ..)
..................
insert c(....) values(x1....xm)