create view t1_t2 (name, serial) as 
values (cast(null as varchar( 10 )), cast(null as varchar( 10 )))@

create trigger t1_t2
instead of insert on t1_t2
referencing new as n
for each row
begin atomic
  declare l_id_ext int;
  
  insert into table1 (id_ext, serial)
  select t2.id_ext, n.serial
  from table2 t2 
  where t2.name=n.name;
  
  -- если нет записи в table2 и надо игнорировать вставку - 
  -- выкиньте из триггера всё (вместе с begin atomic и end), 
  -- исключая предыдущий insert
  set l_id_ext = (
  select id_ext
  from new table (
  insert into table2 (name)
  select name
  from table(values n.name) n(name)
  where not exists (select  1  from table2 t2 where t2.name=n.name)
  ));
  
  if (l_id_ext is not null) then
    insert into table1 (id_ext, serial) values (l_id_ext, n.serial);
  end if;
end
@

IMPORT FROM "file" OF DEL METHOD P ( 2 ,  3 ) MESSAGES "err" INSERT INTO t1_t2 

create table t1_t2_t (name varchar( 10 ), serial varchar( 10 )) in userspace1@
create view t1_t2 (name, serial) as select name, serial from t1_t2_t@
create trigger t1_t2 ... @