function to check whether a number is prime or not

prime.sql

-- 1 is treated as prime as per this function.

create function is_prime(num integer) returns boolean as $$
begin -- begin block;
  for i in 2..(num/2) loop 
    if num % i = 0 then 
      return false; -- return false if it's get divided by any number smaller than half of it or half itself.
    end if;
  end loop;
  return true;
end; $$
language plpgsql;