recreate view v_all as select current_date dt from rdb$database;
recreate table t01(dt date unique check( extract(month from dt)=1 ) );
recreate table t02(dt date unique check( extract(month from dt)=2 ));
recreate table t03(dt date unique check( extract(month from dt)=3 ));
commit;
recreate view v_all as
select dt from t01
union all
select dt from t02
union all
select dt from t03;
commit;
insert into t01 values('22.01.2014');
insert into t01 values('28.01.2014');
insert into t02 values('02.02.2014');
insert into t02 values('15.02.2014');
insert into t03 values('07.03.2014');
insert into t03 values('23.03.2014');
commit;
set term ^;
create or alter trigger v_all_bu for v_all active before update as
  declare m smallint;
  declare d smallint;
begin
  m = extract(month from new.dt);
  if (m=1) then update t01 set dt=new.dt where dt=old.dt;
  if (m=2) then update t02 set dt=new.dt where dt=old.dt;
  if (m=3) then update t03 set dt=new.dt where dt=old.dt;
end
^set term ;^
commit;

update v_all set dt=dateadd(-1 year to dt);
select v.* from v_all v;