对 Snowflake 中的上一行和当前行值执行数学运算

Question

我有一个要求，我需要对 Snowflake 中列的先前值和当前值执行一些数学计算。

例如：

我的 Snowflake table 有如下数据

此处CHANGE_IN_FRUIT_COUNT和CHANGE_IN_VEG_COUNT字段计算如下

((current_val/previous_val)*100)-100

我也想在我的 table 中实现相同的逻辑。

Answer 1

使用 LAG：

SELECT DATE, 
   (FRUITS_SOLD / LAG(FRUITS_SOLD) 
                      OVER(ORDER BY DATE))*100-100 AS CHANGE_IN_FRUIT_COUNT.
   (VEGETABLE_SOLD / LAG(VEGETABLE_SOLD ) 
                      OVER(ORDER BY DATE))*100-100 AS CHANGE_IN_VEG_COUNT
FROM tab
ORDER BY DATE;

db<>fiddle demo

Answer 2

SELECT 
    date,
    fruits_sold,
    vegetable_sold,
    lag(vegetable_sold) over (order by date) as prev_vegetable_sold,
    lag(fruits_sold) over (order by date) as prev_fruits_sold,
    ((vegetable_sold/prev_vegetable_sold)*100)-100 as change_in_veg_count,
    ((fruits_sold/prev_fruits_sold)*100)-100 as change_in_fruit_count
    
FROM VALUES
    ('2022-01-01'::date, 18, 11)
    ,('2022-01-02'::date, 20, 16)
    ,('2022-01-03'::date, 25, 40)
    ,('2022-01-04'::date, 12, 14)
    ,('2022-01-05'::date, 18, 6)
    d(date, fruits_sold, vegetable_sold);

给出：

DATE	FRUITS_SOLD	VEGETABLE_SOLD	PREV_VEGETABLE_SOLD	PREV_FRUITS_SOLD	CHANGE_IN_VEG_COUNT	CHANGE_IN_FRUIT_COUNT
2022-01-01	18	11
2022-01-02	20	16	11	18	45.4545	11.1111
2022-01-03	25	40	16	20	150	25
2022-01-04	12	14	40	25	-65	-52
2022-01-05	18	6	14	12	-57.1429	50

显示了如何使用 LAG 获取先验值。如果您真的不需要为其他事情重用该值，您可以将其捆绑到一行中，如 Lukasz 所示：

SELECT 
    date,
    ((vegetable_sold/lag(vegetable_sold) over (order by date))*100)-100 change_in_veg_count,
    ((fruits_sold/lag(fruits_sold) over (order by date))*100)-100 change_in_fruit_count
FROM VALUES
    ('2022-01-01'::date, 18, 11)
    ,('2022-01-02'::date, 20, 16)
    ,('2022-01-03'::date, 25, 40)
    ,('2022-01-04'::date, 12, 14)
    ,('2022-01-05'::date, 18, 6)
    d(date, fruits_sold, vegetable_sold);

DATE	CHANGE_IN_VEG_COUNT	CHANGE_IN_FRUIT_COUNT
2022-01-01
2022-01-02	45.4545	11.1111
2022-01-03	150	25
2022-01-04	-65	-52
2022-01-05	-57.1429	50

对 Snowflake 中的上一行和当前行值执行数学运算

Perform Math operations on previous and current row value in Snowflake

sql

snowflake-cloud-data-platform