How to Generate Random number without repeat in database using PHP?

SELECT FLOOR(RAND() * 99999) AS random_num
FROM numbers_mst 
WHERE "random_num" NOT IN (SELECT my_number FROM numbers_mst)
LIMIT 1

What this does:

1. Selects random number between 0 – 1 using RAND().
2. Amplifies that to be a number between 0 – 99999.
3. Only chooses those that do not already exist in table.
4. Returns only 1 result.