If a constant integer argument N is specified, it is used as the seed value, which produces a repeatable sequence of column values.
mysql> mysql> SELECT RAND(); +------------------+ | RAND() | +------------------+ | 0.72570215698863 | +------------------+ 1 row in set (0.00 sec) mysql> mysql> SELECT RAND(20); +------------------+ | RAND(20) | +------------------+ | 0.15888261251047 | +------------------+ 1 row in set (0.00 sec) mysql> mysql> SELECT RAND(20); +------------------+ | RAND(20) | +------------------+ | 0.15888261251047 | +------------------+ 1 row in set (0.00 sec) mysql> mysql> SELECT RAND(); +------------------+ | RAND() | +------------------+ | 0.49934750655605 | +------------------+ 1 row in set (0.00 sec) mysql> mysql> SELECT RAND(); +------------------+ | RAND() | +------------------+ | 0.31963109254803 | +------------------+ 1 row in set (0.00 sec)