如何在多对多关系中获取同一输出行上的前 3 条记录

【问题标题】：How to get top 3 records on the same output row in a many to many relationship如何在多对多关系中获取同一输出行上的前 3 条记录
【发布时间】：2023-01-23 02:19:10
【问题描述】：

谁能帮我解决这个 SQL 查询问题？假设下表：

student: student_id, first_name, last_name, age
classes: class_id, class_name
student_classes: class_id, student_id     # junction table

我正在尝试构建一个查询以从每个班级中选择前 3 名最年长的学生。输出如下：

class_id, class_name, top1_first_name, top1_age, top2_first_name, top2_age, top3_first_name, top3_age

我坚持如何在同一输出行上显示这样的输出

【问题讨论】：

标签： mysql sql

【解决方案1】：

SELECT
    classes.class_id,
    classes.class_name,
    (SELECT first_name FROM student WHERE student.student_id = top1.student_id) AS top1_first_name,
    top1.age AS top1_age,
    (SELECT first_name FROM student WHERE student.student_id = top2.student_id) AS top2_first_name,
    top2.age AS top2_age,
    (SELECT first_name FROM student WHERE student.student_id = top3.student_id) AS top3_first_name,
    top3.age AS top3_age
FROM
    classes
    JOIN student_classes ON classes.class_id = student_classes.class_id
    JOIN (SELECT student_id, age FROM student ORDER BY age DESC LIMIT 3) top1 ON top1.student_id = student_classes.student_id
    JOIN (SELECT student_id, age FROM student ORDER BY age DESC LIMIT 3 OFFSET 1) top2 ON top2.student_id = student_classes.student_id
    JOIN (SELECT student_id, age FROM student ORDER BY age DESC LIMIT 3 OFFSET 2) top3 ON top3.student_id = student_classes.student_id
GROUP BY classes.class

【讨论】：