多GROUP BY和BY

Question

依賴於第一組的結果，選擇值，我得到了以下數據庫表：

combination_id | weight | group | std 
------------------------------------------------- 
    1   | 50  | 3  | 7 
    2   | 30  | 3  | 19 
    3   | 30  | 3  | 19 
    4   | 25  | 4  | 7 

I組由列條目組和STD和總結值

SELECT SUM(weight) as weight_sum, group, std FROM weight_table 
WHERE combination_id IN (1, 2, 3) 
GROUP BY group, std 
ORDER BY weight_sum DESC; 

結果看起來是這樣的：

的 重量列

weight | group | std 
----------------------------------------------- 
    60  | 3  | 19 
    50  | 3  | 7 
    25  | 4  | 7 

現在我想要做的第二GROUP BY，但僅在組列，總結在重量列。結果中的std列的值應該是最後一個查詢中權重最高且分組相同的條目的std列的值。 因此，對於組我想爲STD要選擇19，爲最高重量爲組：

weight | group | std 
----------------------------------------------- 
    110  | 3  | 19 
    25  | 4  | 7 

我怎樣才能做到這一點？ 我使用SQLite 3

Answer 1

我想你想要這樣的：

SELECT SUM(weight) as weight_sum, group, max(std) as std FROM weight_table 
WHERE combination_id IN (1, 2, 3) 
GROUP BY group 
ORDER BY weight_sum DESC; 

換句話說，不要認爲這是「多重分組依據」。把它看作是一個單一的聚合，你可以同時得到權重的總和和最大值std。

編輯：

我似乎誤解了這個問題。這在SQL lite中有點痛苦。以下是一種方法：

with w as (
     SELECT SUM(weight) as weight_sum, group, std 
     FROM weight_table 
     WHERE combination_id IN (1, 2, 3) 
     GROUP BY group, std 
    ), 
    wmax as (
     SELECT group, MAX(weight_sum) as maxws 
     FROM w 
     GROUP BY gruop 
    ) 
select w.group, sum(w.weight_sum) as weight_sum, 
     max(case when w.weight_sum = wmax.weight_sum then std end) as std 
from w left join 
    wmax 
    on w.group = wmax.group 
group by w.group 
order by weight_sum DESC;