Calculating age from dob in PostgreSQL using trigger [closed] - postgresql

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I am trying to calculate the age of a person when a record is inserted or updated in table staff but somehow the below trigger function does not work:
create or replace function Age()
returns trigger as $body$
declare
dob1 date;
age1 integer;
BEGIN
select dob into dob1 from staff;
select age(current_date,dob) into age1;
update staff set age=age1;
END; $body$ language plpgsql;
create trigger trig_age
before insert or update on staff
FOR EACH ROW
execute procedure age();
I'm not sure about this above code. I want a trigger to calculate and insert the AGE when inserting DOB in some table

Answer 1

First of all, the name of the trigger function may not be the most appropriate. There is already an overloaded regular function by that name and while the parameters differ and PostgreSQL will therefore accept it, you might confuse whomever has to work with your code.
Otherwise you are not far off. The principal change is that you should not call an UPDATE in a trigger function for the same table that the trigger is fired for: you may get an infinite loop. Just use assignments to the NEW implicit parameter. Since you obviously want the age in years of a person, you should get that specific date_part() into field age.
CREATE OR REPLACE FUNCTION age_in_years() RETURNS TRIGGER AS $body$
BEGIN
NEW.age := date_part('year', CURRENT_TIME - NEW.dob::timestamp);
RETURN NEW; -- or the insert or update would fail
END;
$body$ LANGUAGE plpgsql;
Setting the values in the NEW parameter and returning that parameter at the end of the function will change the values that will be inserted or updated into the table.
However, a person's age may change in between updates so you are probably better off dropping the column age from table staff (and thus also the trigger) and then creating a view that calculates the age whenever that view is accessed:
CREATE VIEW staff_today AS
SELECT *, date_part('year', CURRENT_TIME - dob::timestamp) AS age
FROM staff;
Like so you will always get the correct age.