Joining tables based on the maximum value

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暖寄归人
暖寄归人 2021-02-08 22:00

Here\'s a simplified example of what I\'m talking about:

Table: students      exam_results
_____________       ____________________________________
| id | name |         


        
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  • 2021-02-08 22:35

    Answering the EDITED question (i.e. to get associated columns as well).

    In Sql Server 2005+, the best approach would be to use a ranking/window function in conjunction with a CTE, like this:

    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;
    

    For an ANSI-SQL compliant solution, a subquery and self-join will work, like this:

    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;
    

    This last one assumes there aren't duplicate student_id/max_score combinations, if there are and/or you want to plan to de-duplicate them, you'll need to use another subquery to join to with something deterministic to decide which record to pull. For example, assuming you can't have multiple records for a given student with the same date, if you wanted to break a tie based on the most recent max_score, you'd do something like the following:

    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;
    

    EDIT: Added proper de-duplicating query thanks to Mark's good catch in comments

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  • 2021-02-08 22:39

    Using 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)
    

    If there is a tied score, the oldest date is returned (change date ASC to date DESC to return the most recent instead).

    Output:

    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
    

    Test bed:

    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)
    

    On MySQL, I think you can change the TOP(1) to a LIMIT 1 at the end of the statement. I have not tested this though.

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  • 2021-02-08 22:45
    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
    
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  • 2021-02-08 22:47

    With Oracle's analytic functions this is easy:

    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;
    
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  • 2021-02-08 22:54
    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
    
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  • 2021-02-08 23:00

    Try this,

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