使用 LAG 比較今天和 7 天前的數據（不是之間）

Question

我目前正在嘗試比較今天和 7 天前的匯總數字（不是今天和 7 天前之間，而是簡單地比較這兩個離散日期）。 我已經有了使用很多子查詢的方法，但是性能很差，我現在正在嘗試優化。

到目前為止，這是我想出的（示例查詢，由於機密性，沒有使用真實的表名和列）：

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)

但是我肯定做錯了，因為在 output 中，previous_sum 出現了 null，當然還有百分比。

關於我做錯了什么的任何想法？ 我以前沒有使用過 LAG，所以它一定是有的。 謝謝！

Answer 1

使用預聚合子查詢的連接。

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 

使用滯后：

    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

如果您只想要 2 個日期（今天和今天 7），那么使用條件聚合和過濾器可以更簡單地完成：

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 window（分析）函數來執行此操作，這應該是最快的方法。 您的實際聚合查詢有點不清楚，但我認為是：

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，請使用：

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;

如果您整天都沒有數據，請使用 window 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;