函数 用法
    YEAR(date)/MONTH(date)/DAY(date) 返回具体的日期值
    HOUR(time)/MINUTE(time)/SECOND(time) 返回具体的时间值
    MONTHNAME(date) 返回月份:January,……
    DAYNAME(date) 返回星期几:MONDAY,TUESDAY……SUNDAY
    WEEKDAY(date) 返回周几,注意,周一是0,周二是1,……周日是6
    QUARTER(date) 返回日期对应的季度,范围1~4
    WEEK(date),WEEKOFYEAR(date) 返回一年中的第几周
    DAYOFYEAR(date) 返回日期是一年中的第几天
    DAYOFMONTH(date) 返回日期位于所在月份的第几天
    DAYOFWEEK(date) 返回周几,注意:周日是1,周一是2……周六是7
    1. SELECT YEAR(CURDATE()),MONTH(CURDATE()),DAY(CURDATE()),
    2. HOUR(CURTIME()),MINUTE(NOW()),SECOND(SYSDATE())
    3. FROM DUAL;
    4. SELECT MONTHNAME('2021-10-26'),DAYNAME('2021-10-26'),WEEKDAY('2021-10-26'),
    5. QUARTER(CURDATE()),WEEK(CURDATE()),DAYOFYEAR(NOW()),
    6. DAYOFMONTH(NOW()),DAYOFWEEK(NOW())
    7. FROM DUAL;