定义和用法
EXTRACT() 函数用于返回日期/时间的单独部分，比如年、月、日、小时、分钟等等。
语法
EXTRACT(unit FROM date)
date 参数是合法的日期表达式。unit 参数可以是下列的值：
| Unit 值 |
|---|
| MICROSECOND |
| SECOND |
| MINUTE |
| HOUR |
| DAY |
| WEEK |
| MONTH |
| QUARTER |
| YEAR |
| SECOND_MICROSECOND |
| MINUTE_MICROSECOND |
| MINUTE_SECOND |
| HOUR_MICROSECOND |
| HOUR_SECOND |
| HOUR_MINUTE |
| DAY_MICROSECOND |
| DAY_SECOND |
| DAY_MINUTE |
| DAY_HOUR |
| YEAR_MONTH |
EXTRACT() 示例
提取年份
select extract(year from now())提取第几周
select extract(weeks from now())提取微秒计时
select extract(second_microsecond from now())从字段中提取相应的时间单位：
SELECT sum(order_amount), EXTRACT(week FROM create_date) AS week,
FROM orders
group by week
where date(create_date)="2012"
讨论区