Question

我有以下表格

|Id| Title  |
|1 |Lesson 1|
|2 |Lesson 2|
|3 |Lesson 3|
|4 |Lesson 4|
|5 |Lesson 5|
|6 |Lesson 6|

|Id|Lesson|Score|
|1 |  2   | 75  |
|2 |  3   | 30  |
|3 |  3   | 90  |

我想获得不同的课程但只有最大值，所以结果将是：

|Lesson|Score|
|  2   | 75  |
|  3   | 90  |

所以在下面的查询中，我在哪里放DISTINCT和MAX来实现这样的结果？

SELECT LessonConclusionData.Lesson, LessonConclusionData.Score
FROM LessonConclusionData INNER JOIN Lessons ON LessonConclusionData.Lesson = Lessons.Id

Answer 1

按课程分组并获得MAX（分数）。

SELECT LessonConclusionData.Lesson, MAX(LessonConclusionData.Score) as MaxScore
FROM LessonConclusionData 
     INNER JOIN Lessons ON LessonConclusionData.Lesson = Lessons.Id
GROUP BY LessonConclusionData.Lesson;

Answer 2

SELECT ID,MAX(SCORE)
FROM tablename
GROUP BY ID`

Answer 3

假设SQL Server版本＆gt; = 2005，此代码（使用公用表表达式）将产生所需的结果：

; with x as (
select Lesson, max(Score) Score
from LessonConclusionData
group by Lesson
)
select y.* from x join LessonConclusionData y on x.Lesson = y.Lesson and x.Score = y.Score
order by y.Lesson

如果您需要显示课程名称，您应该加入课程表，如下所示：

; with x as (
select Lesson, max(Score) Score
from LessonConclusionData
group by Lesson
)
select y.*, Lessons.Title from x join LessonConclusionData y on x.Lesson = y.Lesson and x.Score = y.Score
right join Lessons on x.Lesson = Lessons.Id
order by y.Lesson

我选择了RIGHT JOIN而不是返回所有课程的结果，即使对于那些没有LessonConclusionData的人也是如此。如果您只想返回存在详细信息的课程，请使用INNER JOIN。

SQL查询以获取具有最大值的不同元素

3 个答案: