Need help on trigger...

Question

i'm the beginner in Oracle, need help on below.
can i use statement like "Select count..." in the before and after update trigger?
i have the "mutating" error when i create the trigger...
pls help

Answer 1

correction - there is no error generated when compile the trigger but errors when the trigger is fired:
/* perform updating on table student*/
update student set company_id = 60 where student_id = 9998;
/* error return by oracle sql plus*/
at line 1:
4091: table SCOTT.STUDENT is mutating, trigger/function may not see it
6512: at "SCOTT.UST_UPDPASSPORTPROGRAM", line 7
6512: at "SCOTT.UST_UPDPASSPORTPROGRAM", line 9
4088: error during execution of trigger 'SCOTT.UST_UPDPASSPORTPROGRAM'
/* trigger script*/
create or replace trigger ust_updPassportProgram
before update
on student
for each row
declare
v_total_Student number;
Dummy number;
/*CURSOR Dummy_cursor (CNo NUMBER) IS*/
/*SELECT company_id FROM company WHERE company_id = CNo;*/
CURSOR Dummy_cursor (CNo NUMBER) IS
SELECT student_id FROM student WHERE student_id = 9998 and company_id = CNo;
begin
OPEN Dummy_cursor (:new.company_id);
FETCH Dummy_cursor INTO Dummy;
IF Dummy_cursor%FOUND THEN
dbms_output.put_line('Dummy found');
end if;
if :new.passport_program = 'Y' then
dbms_output.put_line('The current company_id: ' ||
to_char(:new.company_id) || :new.passport_program);
end if;
end;
/