EXTRACT
描述
extract 函数用于从日期或时间值中提取指定的部分，如年份、月份、日、小时、分钟、秒等。该函数常用于从日期时间字段中提取具体的时间组件进行计算、比较或展示。
语法
EXTRACT(<unit> FROM <datetime>)
参数
| 参数 | 说明 |
|---|---|
unit | 提取 DATETIME 某个指定单位的值。单位可以为 year, month, day, hour, minute, second 或者 microsecond |
datetime | 参数是合法的日期表达式 |
返回值
返回的是提取出的日期或时间的某个部分（如整数），具体的部分取决于提取的单位。
举例
select extract(year from '2022-09-22 17:01:30') as year,
extract(month from '2022-09-22 17:01:30') as month,
extract(day from '2022-09-22 17:01:30') as day,
extract(hour from '2022-09-22 17:01:30') as hour,
extract(minute from '2022-09-22 17:01:30') as minute,
extract(second from '2022-09-22 17:01:30') as second,
extract(microsecond from cast('2022-09-22 17:01:30.000123' as datetimev2(6))) as microsecond;+------+-------+------+------+--------+--------+-------------+
| year | month | day | hour | minute | second | microsecond |
+------+-------+------+------+--------+--------+-------------+
| 2022 | 9 | 22 | 17 | 1 | 30 | 123 |
+------+-------+------+------+--------+--------+-------------+