语法:date_sub(date,interval expr type),函数从日期减去指定的时间间隔,
举例:Orders 表中 OrderDate 字段减去 2 天:
select OrderId,date_sub(OrderDate,interval 2 day) as OrderPayDate
from Orders
date_sub('2019-07-27', interval 30 day)表示往前推30天
select activity_date day, count(distinct user_id) active_users
from activity
where activity_date > date_sub('2019-07-27', interval 30 day)
and activity_date <= '2019-07-27'
group by activity_date