獲得7天的數據與蜂巢

Question

我有不同的日期一個表

2014-11-20 
2014-12-12 
2014-11-10 
2014-12-13 
2014-10-12 
2016-01-15 
2016-01-14 
2016-01-16 
2016-01-18 

想過去7天的數據（最大日-7）

2016-01-15 
2016-01-14 
2016-01-16 
2016-01-18 

我有試過下面的查詢，但沒有不行

select * from date_txt1 where DATEDIFF((select max(purchase_date) from date_txt1),(select min(purchase_date) from date_txt1)) <= 7; 

Answer 1

在 「DATEDIFF」 作爲第二個參數使用單純的列名：

select * from date_txt1 
where DATEDIFF((select max(purchase_date) from date_txt1), purchase_date) <= 7; 

更新：「最大」提取：

with maxDate as (
    select max(purchase_date) as end_date 
    from date_txt1 
) 
Select * 
From date_txt1 , maxDate 
where DATEDIFF(maxDate.end_date, purchase_date) <= 7; 

Answer 2

select a.purchase_date 
from date_txt1 a 
cross join (select max(purchase_date) as maxdate from date_txt1) b 
where DATEDIFF(b.maxdate, a.purchase_date) <= 7