SUM() 基于与 SELECT 不同的条件

Question

嗨，有没有一种方法可以根据与 SELECT 语句的其余部分不同的条件来执行 SUM(total_points)，所以我想要

非常感谢您的帮助。

SELECT
    members.member_id,
    members.teamname,
    SUM(total_points) as total_points,
    total_points as last_race_points 
FROM
    members,
    members_leagues,
    member_results 
WHERE
    members.member_id = members_leagues.member_id 
    AND members_leagues.league_id = '$chosenleague' 
    AND member_results.track_id = '$chosentrack' 
    AND members_leagues.start_race = '$chosentrack' 
    AND member_results.member_id = members_leagues.member_id
GROUP BY
    members.member_id 
ORDER BY
    member_results.total_points DESC,
    last_race_points DESC, 
    members.teamname DESC

Answer 1

您还可以将总和放在 case 语句中，其中 case 评估另一个条件，然后仅对条件为真的那些记录求和...

  SELECT m.member_id, m.teamname, 
    Sum(Case When r.track_Id = '$chosentrack' 
         Then total_points Else 0 End) TotalChosenTrackPoints,
    Sum(Case When r.track_Id < '$chosentrack' 
         Then total_points Else 0 End) TotalLessThanChosenTrackPoints, 
    total_points as last_race_points  
 FROM members m
    Join members_leagues l
       On l.member_id = m.member_id  
    Join member_results r
       On r.member_id = m.member_id
 Where l.league_id = '$chosenleague'
    And l.start_race = '$chosentrack'
 Group By m.member_id
 Order By r.total_points Desc, 
     last_race_points  Desc, m.TeamName Desc  

Answer 2

SELECT ... 
SUM(CASE
WHEN track_id <= [your_value] THEN total_points
ELSE 0
END
) AS total_points, .... 

Answer 3

将求和作为子选择进行，确保选择了附加列（不要忘记按该列分组）并使用公共字段将此子选择的结果连接到主查询。

模板：

Select col1, 
col2 as t,x.thesum
From table t left join 
( select sum(colx) as thesum, col1 from t where ...
 Group by col1) x on t.col1=x.col1
 Where ....