You may optionally put a SEED value in as a param to get the same result.
For example if you want the same random value to be used multiple times in a single select or batch you would seed them all with the same value. Repetitive calls of RAND() with the same seed value, during a single query, are guaranteed to return the same results.
SELECT RAND() RETURNS: 0.15155745910087481 (This will be different each time you run it) Optional param: SELECT RAND(100) RETURNS: 0.9687746888812514 (This should be the same since it has a seed value)