Oracle PL/SQL check an input against 3 constants

I need to check a variable (Subject Name) and make sure that it is 1 of the following before inserting or updating - Software, Computing or Business.

This is for a piece of Uni work and the lecturers are awful so any help would be appreciated.

I have the following code but it does not seem to work.

create or replace trigger subject_name_check
  before insert or update on Student
  FOR EACH ROW
  WHEN (NEW.SUBJECT <> 'Software' or 'Computing' or 'Business')
begin
  DBMS_OUTPUT.PUT_LINE('INVALID INPUT');
end;

Solution

All you are doing is printing a message, which the client may or may not be configured to see. You aren't stopping the insert from completing.

You could raise an exception instead:

create or replace trigger subject_name_check
  before insert or update on Student
  FOR EACH ROW
  WHEN (NEW.SUBJECT NOT IN ('Software', 'Computing', 'Business'))
begin
  RAISE_APPLICATION_ERROR(-20001, 'INVALID INPUT');
end;

I fixed the comparison logic too - you can't compare one thing with multiple others in the way you had attempted.

Quick demo:

create table student (subject varchar2(20));

create or replace trigger subject_name_check
  before insert or update on Student
  FOR EACH ROW
  WHEN (NEW.SUBJECT NOT IN ('Software', 'Computing', 'Business'))
begin
  RAISE_APPLICATION_ERROR(-20001, 'INVALID INPUT');
end;
/

insert into student (subject) values ('Software');

1 row inserted.

insert into student (subject) values ('Spanish');

ORA-20001: INVALID INPUT
ORA-06512: at "MYSCHEMA.SUBJECT_NAME_CHECK", line 2

But this should really be done with a check constraint, not with a trigger:

drop trigger subject_name_check;

alter table student add (
  constraint subject_name_check check (
    subject in ('Software', 'Computing', 'Business'))
);

insert into student (subject) values ('Computing');

1 row inserted.

insert into student (subject) values ('Physics');

ORA-02290: check constraint (MYSCHEMA.SUBJECT_NAME_CHECK) violated

... or even better with a foreign key relationship to another table with a valid list of subjects.