mysql 内置函数-日期函数

6.8 mysql 内置函数-日期函数

6.8.1 当前日期 – curdate()

    mysql> select curdate();
    +------------+
    | curdate()  |
    +------------+
    | 2018-02-12 |
    +------------+
    1 row in set (0.00 sec)

6.8.2 当前时间 – curtime()

    mysql> select curtime();
    +-----------+
    | curtime() |
    +-----------+
    | 22:41:57  |
    +-----------+
    1 row in set (0.00 sec)

6.8.3 当前日期和时间 – now()

    mysql> select now();
    +---------------------+
    | now()               |
    +---------------------+
    | 2018-02-12 22:42:23 |
    +---------------------+
    1 row in set (0.00 sec)

6.8.4 unix时间戳 – unix_timestamp()

    mysql> select unix_timestamp();
    +------------------+
    | unix_timestamp() |
    +------------------+
    |       1518504183 |
    +------------------+
    1 row in set (0.00 sec)

6.8.5 unix的日期值 – from_unixtime(date)

    mysql> select from_unixtime(1518504183);
    +---------------------------+
    | from_unixtime(1518504183) |
    +---------------------------+
    | 2018-02-12 22:43:03       |
    +---------------------------+
    1 row in set (0.00 sec)

6.8.6 一年中的第几周 – week(date)

    mysql> select week('2018-02-13');
    +--------------------+
    | week('2018-02-13') |
    +--------------------+
    |                  6 |
    +--------------------+
    1 row in set (0.00 sec)

    mysql> select week(now());
    +-------------+
    | week(now()) |
    +-------------+
    |           6 |
    +-------------+
    1 row in set (0.00 sec)

6.8.7 日期的年份、月份、日期 – year(date)、month(date)、day(date)

    mysql> select now();
    +---------------------+
    | now()               |
    +---------------------+
    | 2018-02-12 22:47:07 |
    +---------------------+
    1 row in set (0.00 sec)

    mysql> select year(now());
    +-------------+
    | year(now()) |
    +-------------+
    |        2018 |
    +-------------+
    1 row in set (0.00 sec)

    mysql> select month(now());
    +--------------+
    | month(now()) |
    +--------------+
    |            2 |
    +--------------+
    1 row in set (0.00 sec)

    mysql> select day(now());
    +------------+
    | day(now()) |
    +------------+
    |         12 |
    +------------+
    1 row in set (0.00 sec)

6.8.8 间隔天数 – datediff(date1,date2)

    mysql> select datediff('2018-02-13','2018-02-14');
    +-------------------------------------+
    | datediff('2018-02-13','2018-02-14') |
    +-------------------------------------+
    |                                  -1 |
    +-------------------------------------+
    1 row in set (0.00 sec)

    mysql> select datediff('2018-02-14','2018-02-13');
    +-------------------------------------+
    | datediff('2018-02-14','2018-02-13') |
    +-------------------------------------+
    |                                   1 |
    +-------------------------------------+
    1 row in set (0.00 sec)

    mysql> select datediff('2018-02-14 12:00:00','2018-02-14 00:00:00');
    +-------------------------------------------------------+
    | datediff('2018-02-14 12:00:00','2018-02-14 00:00:00') |
    +-------------------------------------------------------+
    |                                                     0 |
    +-------------------------------------------------------+
    1 row in set (0.00 sec)

    mysql> select datediff('2018-02-14 12:00:00','2018-02-13 23:59:59');
    +-------------------------------------------------------+
    | datediff('2018-02-14 12:00:00','2018-02-13 23:59:59') |
    +-------------------------------------------------------+
    |                                                     1 |
    +-------------------------------------------------------+
    1 row in set (0.00 sec)

    mysql> select datediff('2018-02-14 12:00:00','2018-02-13 00:00:00');
    +-------------------------------------------------------+
    | datediff('2018-02-14 12:00:00','2018-02-13 00:00:00') |
    +-------------------------------------------------------+
    |                                                     1 |
    +-------------------------------------------------------+
    1 row in set (0.00 sec)

    mysql> select datediff('2018-02-14 12:00:00','2018-02-13 02:00:00');
    +-------------------------------------------------------+
    | datediff('2018-02-14 12:00:00','2018-02-13 02:00:00') |
    +-------------------------------------------------------+
    |                                                     1 |
    +-------------------------------------------------------+
    1 row in set (0.00 sec)

    mysql> select datediff('2018-02-14 12:00:00','2018-02-13 12:00:00');
    +-------------------------------------------------------+
    | datediff('2018-02-14 12:00:00','2018-02-13 12:00:00') |
    +-------------------------------------------------------+
    |                                                     1 |
    +-------------------------------------------------------+
    1 row in set (0.00 sec)


    mysql> select datediff('2018-02-14 12:00:00','2018-02-12 12:00:00');
    +-------------------------------------------------------+
    | datediff('2018-02-14 12:00:00','2018-02-12 12:00:00') |
    +-------------------------------------------------------+
    |                                                     2 |
    +-------------------------------------------------------+
    1 row in set (0.00 sec)

    结论：该函数只是计算间隔天数，不足一天也是间隔一天