如果我们尝试仅通过向MySQL EXTRACT()函数提供日期值来提取时间值，将会输出什么？
当我们尝试从日期中提取小时值时，EXTRACT()函数将为输出0提供警告，如以下示例所示-
mysql> Select EXTRACT(Hour from '2017-10-20'); +---------------------------------+ | EXTRACT(Hour from '2017-10-20') | +---------------------------------+ | 0 | +---------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> Show Warnings; +---------+------+----------------------------------------------+ | Level | Code | Message | +---------+------+----------------------------------------------+ | Warning | 1292 | Truncated incorrect time value: '2017-10-20' | +---------+------+----------------------------------------------+ 1 row in set (0.00 sec)
现在，当我们尝试从日期中提取分钟值时，EXTRACT()函数将给出带有日期的世纪值作为输出，并带有警告，如以下示例所示：
mysql> Select EXTRACT(Minute from '2017-10-20'); +-----------------------------------+ | EXTRACT(Minute from '2017-10-20') | +-----------------------------------+ | 20 | +-----------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> Show Warnings; +---------+------+----------------------------------------------+ | Level | Code | Message | +---------+------+----------------------------------------------+ | Warning | 1292 | Truncated incorrect time value: '2017-10-20' | +---------+------+----------------------------------------------+ 1 row in set (0.00 sec)
现在，当我们尝试从日期中提取秒值时，EXTRACT()函数将以警告的形式给出年份的值，如下面的示例所示-
mysql> Select Extract(Second from '2017-10-20'); +-----------------------------------+ | Extract(Second from '2017-10-20') | +-----------------------------------+ | 17 | +-----------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> Show Warnings; +---------+------+----------------------------------------------+ | Level | Code | Message | +---------+------+----------------------------------------------+ | Warning | 1292 | Truncated incorrect time value: '2017-10-20' | +---------+------+----------------------------------------------+ 1 row in set (0.00 sec)
尝试从当前日期获取时间值（小时，分钟和秒），即Curdate()在日期位置使用，我们将获得类似的结果。
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