MICROSECOND(expr)
返回从时间或日期时间表达式expr的微秒，范围从0到999999的数字。
mysql> SELECT MICROSECOND('12:00:00.123456'); +---------------------------------------------------------+ | MICROSECOND('12:00:00.123456') | +---------------------------------------------------------+ | 123456 | +---------------------------------------------------------+ 1 row in set (0.00 sec)
