To react action in each row, you need to use row-level triggers.
The following trigger implements a rule: A manager may not receive a commission that exceeds his or her salary.
This rule is about the data in each row, so it should be implemented as row-level trigger.
In row-level triggers is that you can use :OLD and :NEW prefixes on each column of the table to reference the original and modified values.
SQL> SQL> drop table emp; Table dropped.-- from w w w . ja va 2s.com Elapsed: 00:00:00.02 SQL> create table emp( 2 empno number(4,0), 3 ename varchar2(10), 4 job varchar2(9), 5 mgr number(4,0), 6 hiredate date, 7 sal number(7,2), 8 comm number(7,2), 9 deptno number(2,0) 10 ); Table created. SQL> SQL> insert into emp values(7839, 'KING', 'PRESIDENT', null, to_date('17-11-1981','dd-mm-yyyy'), 5000, null, 10); SQL> insert into emp values(7698, 'BLAKE', 'MANAGER', 7839,to_date('1-5-1981','dd-mm-yyyy'), 2850, null, 30); SQL> create or replace trigger emp_biu 2 before insert or update 3 on emp 4 referencing new as new old as old 5 for each row 6 begin 7 if :new.job = 'MANAGER' 8 and nvl(:new.sal,0)<nvl(:new.comm,0) then 9 raise_application_error (-20999,'Managers should 10 not have commissions higher then salary!'); 11 end if; 12 end; 13 / SQL>