Question

I am writing a trigger to check if an employee is allocated to two flights that overlap.

It would be something like:

select flight_id from flight 
where arrival_time > :new.departure_time
and departure_time < :new.arrival_time;

if flight_id is empty 
  [do nothing]
if flight_id exists
  [raise application error]

Can anyone help me out in how I would have to code the conditional logic there? This is my first time working with oracle (university coursework).

Answer 1

SELECT ... INTO is your friend. It will raise an exception, you catch it, do nothing, otherwise and raise your own error.

select flight_id into v
from flight 
where arrival_time > :new.departure_time
and departure_time < :new.arrival_time;
raise_application_error(-20000, 'not good');
exception
when NO_DATA_FOUND
  then return 1
 when others
   then raise_application_error(-20011,'really good');