Invoking procedure from a trigger to validate birthdate - sql

Question

I have created a trigger below (Trig 1)to fire before insert on employee table. Then this trigger will invoke the procedure (Proc 1) which will validate the birthdate being not earlier the the current date. if not proceed with the insert, but if date is earlier than current date, it will show a message like "invalid birthdate".
(Trig 1)
create or replace trigger VALIDATE_BDAY_TRIG
before insert on employee
for each row
declare
birth_date date;
employee_birthdate date;
begin
birth_date := employee_birthdate;
val_bday_proc birth_date;
end VALIDATE_BDAY_TRIG;
(Proc 1)
create or replace procedure val_bday_proc(
date_of_birth in date)
as
begin
if date_of_birth > current_date()
then raise_application_error(-20000, 'Employee birth date should not be earlier than the current date');
end;

Answer 1

When calling a stored procedure, you should pass variables between parentheses:
val_bday_proc(birth_date)
Also, you need to get the actual value that is to be inserted, because now employee_birthdate is just a variable, and will be null. You can use :new.fieldname to get the value of the field 'fieldname' of the new record. No need to declare variables for that at all, so your trigger could look like this, assuming the field is called employee_birthdate:
Create or Replace trigger VALIDATE_BDAY_TRIG
before insert on employee
for each row
begin
val_bday_proc(:new.employee_birthdate);
end VALIDATE_BDAY_TRIG;
The stored procedure seems to be okay, except it's missing the end if; to close the if-statement.
Some side notes:
You seem to be confusing earlier and later. The code in the proc is okay, but in the error message and in your question text you got it the other way around.
You could (maybe should?) also check this on update, otherwise you can insert an earlier date and then update it to some date in the future. You could make a separate trigger for this, or modify the current one to also trigger on update: (before insert or update).
It may help to have a naming convention for triggers that show their context (whether they are insert and/or update, row level or statement level). That helps you find the right one if you have multiple triggers.
It's a good idea to at least consider not putting this in a trigger at all. I learned the hard way that having a lot of business logic in triggers will eventually affect performance, is hard to debug, and hard to change. These kind of checks could be made in an application layer that stores the employee-data.