使用LAG来比较今天和7天前的数据(而不是两者之间的数据)

Question

我目前正在尝试比较今天和正好7天前的汇总数字(不是今天和7天前，而是简单地比较这两个离散日期(。我已经有了一种使用大量子查询的方法，但性能很差，我现在正在尝试优化。

这就是我到目前为止所想到的(示例查询，由于保密性，没有使用真实的表名和列(：

Select current_date, previous_date, current_sum, previous_sum, percentage
From   (Select date as current_date, sum(numbers) as current_sum, 
lag (sum(numbers)) over (partition by date order by date) as previous_sum,
(Select max(date)-7 From t1 ) as previous_date,
(current_sum - previous_sum)*100/current_sum as percentage
From t1 where date>=sysdate-7 group by date,previous_date)

但我肯定做错了什么，因为在输出中，previous_sum显示为空，当然百分比也显示为空。

你知道我做错了什么吗？我以前没有用过LAG，所以肯定有什么东西。谢谢

Answer 1

使用预聚合子查询的Join。

with agg as (
select sum(numbers) as sum_numbers, date from t1 group by date
)
select curr.sum_numbers as current_sum, 
prev.sum_numbers as prev_sum, 
curr.date        as curr_date, 
prev.date        as prev_date
from agg curr
left join agg prev on curr.date-7=prev.date 

使用滞后：

with agg as (
select sum(numbers) as sum_numbers, date from t1 group by date
)
select sum_numbers       as current_sum, 
lag(sum_numbers, 7) over(order by date)  as prev_sum,
a.date            as curr_date,
lag(a.date,7) over(order by date) as prev_date
from agg a

如果你只想要两个日期(今天和今天-7(，那么使用条件聚合和过滤器可以简单得多：

select sum(case when date = trunc(sysdate) then numbers else null end) as current_sum, 
sum(case when date = trunc(sysdate-7) then numbers else null end) as previous_sum, 
trunc(sysdate)         as curr_date, 
trunc(sysdate-7)       as prev_date,
(current_sum - previous_sum)*100/current_sum as percentage
from t1 where date = trunc(sysdate) or date = trunc(sysdate-7)

Answer 2

您可以使用窗口(分析(函数来实现这一点，这应该是最快的方法。您的实际聚合查询有点不清楚，但我认为它是：

select date as current_date, sum(numbers) as current_sum
from t1 
group by date;

如果您有所有日期的值，则使用：

select date as current_date, sum(numbers) as current_sum, 
lag(sum(numbers), 7) over (order by date) as prev_7_sum
from t1 
group by date;

如果你没有整天的数据，那么使用一个窗口框架：

select date as current_date, sum(numbers) as current_sum, 
max(sum(numbers), 7) over (order by date range between '7' day preceding and '7' day preceding) as prev_7_sum
from t1 
group by date;