在 Snowflake 查询中使用 window 函数进行条件分组

Question

我在 Snowflake 中有一个 table，格式如下：

create temp_test(name string, split string, value int)

insert into temp_test
values ('A','a', 100), ('A','b', 200), ('A','c',300), ('A', 'd', 400), ('A', 'e',500), ('B', 'a', 1000), ('B','b', 2000), ('B','c', 3000), ('B', 'd',4000), ('B','e', 5000)

第一步，我只需要 每个名称的前 2 个值（按值排序），所以我使用以下查询来获取：

select name, split, value,
row_number() over (PARTITION BY (name) order by value desc) as row_num 
from temp_test
qualify row_num <= 2

这给了我以下结果集：

NAME    SPLIT   VALUE   ROW_NUM
A       e       500     1
A       d       400     2
B       e       5000    1
B       d       4000    2

现在，我需要对 Top 2 以外的值求和并将其放入名为 "Others" 的不同拆分中，如下所示：

NAME    SPLIT   VALUE   
A       e       500     
A       d       400     
A       Others  600        
B       e       5000    
B       d       4000
B       Others  6000

如何在 Snowflake 查询或 SQL 中执行此操作？

Answer 1

with data as (
    select name, split, value,
        row_number() over (partition by (name) order by value desc) as row_num 
    from temp_test
)
select
    name,
    case when row_num <= 2 then split else 'Others' end as split,
    sum(value) as value
from data
group by name, case when row_num <= 2 then row_num else 3 end

Answer 2

Shawnt00的回答很好，但是为了记录在Snowflake中这个可以写得更简单：

首先末尾的group by可以通过index或者name来引用结果：

GROUP BY 1,2

或

GROUP BY name, split

此外，由于 CASE 只有太多分支，因此可以使用 IFF，并且您似乎正在使用 CTE 添加 row_number 您也可以将 IFF 推入 CTE

WITH data AS (
    SELECT name, value,
        ROW_NUMBER() OVER (PARTITION BY name ORDER BY value DESC) AS row_num,
        IFF(row_num < 3, split, 'Others') as n_split
    FROM VALUES ('A','a', 100), ('A','b', 200), ('A','c',300), ('A', 'd', 400), 
                ('A', 'e',500), ('B', 'a', 1000), ('B','b', 2000), ('B','c', 3000), 
                ('B', 'd',4000), ('B','e', 5000) 
    v(name, split, value)
)   
SELECT
    name,
    n_split,
    SUM(value) AS value
FROM data
GROUP BY name, n_split;

如果超级热衷于小 SQL 将 ROW_NUMBER 推入 IFF：

WITH data AS (
    SELECT name, value,
        IFF(ROW_NUMBER() OVER (PARTITION BY name ORDER BY value DESC) < 3, split, 'Others') as n_split
    FROM VALUES ('A','a', 100), ('A','b', 200), ('A','c',300), ('A', 'd', 400), 
                ('A', 'e',500), ('B', 'a', 1000), ('B','b', 2000), ('B','c', 3000), 
                ('B', 'd',4000), ('B','e', 5000) 
    v(name, split, value)
)   
SELECT
    name,
    n_split AS split,
    SUM(value) AS value
FROM data
GROUP BY name, n_split;

给出：

NAME    SPLIT   VALUE
A       e       500
A       d       400
A       Others  600
B       e       5000
B       d       4000
B       Others  6000

在 Snowflake 查询中使用 window 函数进行条件分组

Conditional group by with window function in Snowflake query

sql

window-functions

snowflake-cloud-data-platform

row-number