时间处理函数 date()

    1. select order_date,cust_id,order_num from orders where date(order_date)="2005-09-01";
    1. +---------------------+---------+-----------+
    2. | order_date          | cust_id | order_num |
    3. +---------------------+---------+-----------+
    4. | 2005-09-01 00:00:00 |   10001 |     20005 |
    5. +---------------------+---------+-----------+

    now() 当前的日期和时间

    1. +---------------------+
    2. | now()               |
    3. +---------------------+
    4. | 2022-01-06 02:12:24 |
    5. +---------------------+

    Day() 返回一个日期是几号
    DayOfWeek() 返回一个日期对应的星期几
    CurTime() 返回当前时间
    CurDate() 返回当前日期
    DateDiff() 计算两个日期之差

    Abs() 取绝对值
    Mod() 取余
    Pi() 圆周率
    Rand() 随机数
    Sqrt() 取平方根