For oracle i have the following solution :

CREATE OR REPLACE TRIGGER PLN_TEST
BEFORE INSERT
ON
TEST
REFERENCING
New AS MyNew
Old AS MyOld
FOR EACH ROW
DECLARE
PRAGMA AUTONOMOUS_TRANSACTION;
v_new_syscode TEST.SYSCODE%TYPE;
BEGIN
if :MyNew.Syscode is null then

PLN_GETNEWID('TEST',v_new_syscode);
commit;
:MyNew.SYSCODE :=v_new_syscode;
end if;
END
;
/

Does someone know how to do this in sybase and mssql