根據最大值連接表

Question

這是我正在談論的簡化示例：

Table: students      exam_results
_____________       ____________________________________
| id | name |       | id | student_id | score |   date |
|----+------|       |----+------------+-------+--------|
|  1 | Jim  |       |  1 |          1 |    73 | 8/1/09 | 
|  2 | Joe  |       |  2 |          1 |    67 | 9/2/09 |
|  3 | Jay  |       |  3 |          1 |    93 | 1/3/09 |
|____|______|       |  4 |          2 |    27 | 4/9/09 |
                    |  5 |          2 |    17 | 8/9/09 |
                    |  6 |          3 |   100 | 1/6/09 |
                    |____|____________|_______|________|

為了這個問題，假設每個學生都至少記錄了一個考試成績。

你會如何選擇每個學生的最高分？ 編輯 ：...和該記錄中的其他字段？

預期產量：

_________________________
| name | score |   date |
|------+-------|--------|
|  Jim |    93 | 1/3/09 |
|  Joe |    27 | 4/9/09 |
|  Jay |   100 | 1/6/09 |
|______|_______|________|

歡迎使用所有類型的DBMS的答案。

Answer 1

回答EDITED問題（即獲得相關列）。

在Sql Server 2005+中，最好的方法是將排名/窗口函數與CTE結合使用，如下所示：

with exam_data as
(
    select  r.student_id, r.score, r.date,
            row_number() over(partition by r.student_id order by r.score desc) as rn
    from    exam_results r
)
select  s.name, d.score, d.date, d.student_id
from    students s
join    exam_data d
on      s.id = d.student_id
where   d.rn = 1;

對於符合ANSI-SQL的解決方案，子查詢和自聯接將起作用，如下所示：

select  s.name, r.student_id, r.score, r.date
from    (
            select  r.student_id, max(r.score) as max_score
            from    exam_results r
            group by r.student_id
        ) d
join    exam_results r
on      r.student_id = d.student_id
and     r.score = d.max_score
join    students s
on      s.id = r.student_id;

最后一個假設沒有重復的student_id / max_score組合，如果有和/或你想要計算去重復它們，你需要使用另一個子查詢加入一個確定性的東西來決定要拉哪個記錄。 例如，假設您不能為具有相同日期的特定學生提供多條記錄，如果您想根據最新的max_score打破平局，您可以執行以下操作：

select  s.name, r3.student_id, r3.score, r3.date, r3.other_column_a, ...
from    (
            select  r2.student_id, r2.score as max_score, max(r2.date) as max_score_max_date
            from    (
                        select  r1.student_id, max(r1.score) as max_score
                        from    exam_results r1
                        group by r1.student_id
                    ) d
            join    exam_results r2
            on      r2.student_id = d.student_id
            and     r2.score = d.max_score
            group by r2.student_id, r2.score
        ) r
join    exam_results r3
on      r3.student_id = r.student_id
and     r3.score = r.max_score
and     r3.date = r.max_score_max_date
join    students s
on      s.id = r3.student_id;

編輯：由於馬克在評論中的好評，添加了正確的重復數據刪除查詢

Answer 2

SELECT s.name,
    COALESCE(MAX(er.score), 0) AS high_score
FROM STUDENTS s
    LEFT JOIN EXAM_RESULTS er ON er.student_id = s.id
GROUP BY s.name

Answer 3

試試這個，

Select student.name, max(result.score) As Score from Student
        INNER JOIN
    result
        ON student.ID = result.student_id
GROUP BY
    student.name

Answer 4

使用Oracle的分析功能，這很容易：

SELECT DISTINCT
       students.name
      ,FIRST_VALUE(exam_results.score)
       OVER (PARTITION BY students.id
             ORDER BY exam_results.score DESC) AS score
      ,FIRST_VALUE(exam_results.date)
       OVER (PARTITION BY students.id
             ORDER BY exam_results.score DESC) AS date
FROM   students, exam_results
WHERE  students.id = exam_results.student_id;

Answer 5

使用MS SQL Server：

SELECT name, score, date FROM exam_results
JOIN students ON student_id = students.id
JOIN (SELECT DISTINCT student_id FROM exam_results) T1
ON exam_results.student_id = T1.student_id
WHERE exam_results.id = (
    SELECT TOP(1) id FROM exam_results T2
    WHERE exam_results.student_id = T2.student_id
    ORDER BY score DESC, date ASC)

如果存在綁定分數，則返回最舊的日期（將date ASC更改為date DESC以返回最近的date DESC ）。

輸出：

Jim 93  2009-01-03 00:00:00.000
Joe 27  2009-04-09 00:00:00.000
Jay 100 2009-01-06 00:00:00.000

試驗台：

CREATE TABLE students(id int , name nvarchar(20) );

CREATE TABLE exam_results(id int , student_id int , score int, date datetime);

INSERT INTO students
VALUES
(1,'Jim'),(2,'Joe'),(3,'Jay')

INSERT INTO exam_results VALUES
(1, 1, 73, '8/1/09'), 
(2, 1, 93, '9/2/09'),
(3, 1, 93, '1/3/09'),
(4, 2, 27, '4/9/09'),
(5, 2, 17, '8/9/09'),
(6, 3, 100, '1/6/09')

SELECT name, score, date FROM exam_results
JOIN students ON student_id = students.id
JOIN (SELECT DISTINCT student_id FROM exam_results) T1
ON exam_results.student_id = T1.student_id
WHERE exam_results.id = (
    SELECT TOP(1) id FROM exam_results T2
    WHERE exam_results.student_id = T2.student_id
    ORDER BY score DESC, date ASC)

在MySQL上，我認為您可以在語句結束時將TOP（1）更改為LIMIT 1。 我沒有測試過這個。

Answer 6

Select Name, T.Score, er. date 
from Students S inner join
          (Select Student_ID,Max(Score) as Score from Exam_Results
           Group by Student_ID) T 
On S.id=T.Student_ID inner join Exam_Result er
On er.Student_ID = T.Student_ID And er.Score=T.Score