Sqlite 使用合并减去列值

我想为race、bib、splitgroupby中返回的每条记录减去place列中的值，这样diff列就会像这样显示

期望输出：

我不熟悉使用coalesce语句，最接近预期输出的是以下内容

select a.race,a.bib,a.split, a.place, 
coalesce(a.place - 
    (select b.place from ranking b where b.split < a.split), a.place) as diff
from ranking a
group by race,bib, split 

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谢谢你的关注

要计算差异，您必须在具有相同种族和bib值的行中查找值，以及下一个较小的分割值：

select a.race,a.bib,a.split, a.place, 
coalesce(a.place - 
    (select b.place from ranking b where b.split < a.split), a.place) as diff
from ranking a
group by race,bib, split 

     race | bib | split | place | diff  
     ----------------------------------
     10   | 514 | 1     | 5     | 5
     10   | 514 | 2     | 3     | 2 
     10   | 514 | 3     | 2     | 1
     10   | 17  | 1     | 8     | 8
     10   | 17  | 2     | 12    | 11
     10   | 17  | 3     | 15    | 14

SELECT race, bib, split, place,
       coalesce((SELECT r2.place
                 FROM ranking AS r2
                 WHERE r2.race  = ranking.race
                   AND r2.bib   = ranling.bib
                   AND r2.split < ranking.split
                 ORDER BY r2.split DESC
                 LIMIT 1
                ) - place,
                0) AS diff
FROM ranking;