sql - Trigger with a function Oracle -

i need make trigger insert 'a' in case of approved student , 'r' not approved student. need use function returns 'a' or 'r'. here function:

create or replace function check_grade (grade in number, frequency in number) return varchar2  result varchar2(1) default ''; begin if(grade>=6) , (frequency>=0.75)then result := 'a'; else result := 'r'; end if; return result; end; 

and here trigger:

create or replace trigger situation before  insert on student each row begin select check_grade(grade, frequency) : new.situation dual; end; 

when try execute error. don't have idea in can do!

user-defined functions allowed in triggers, , function looks ok.

one definite problem trigger mentions grade , frequency, variable names, , haven't been declared. i'll assume meant use inserted column values instead: :new.grade , :new.frequency.

also, i've set "new" values using simple variable assignment (:new.value := blah instead of select blah :new.value dual). way may work (or may not - don't know), simple variable assignment syntax lot shorter , it's easy enough read.

so try replacing these 3 lines:

select check_grade(grade, frequency) : new.situation dual; 

... 1 line:

:new.situation := check_grade(:new.grade, :new.frequency); 

if doesn't work please update question , replace "i error" i error ora-<actual-error-number>. include stack trace, show if function or trigger throwing.