Question

我有两张桌子：

teachers (teacher_id,teacher_name)
courses (teacher_id,course_id)

我需要显示教师的姓名，教授最多课程数量：

的MySQL＆GT;选择teachers.teacher_name，tmp1.teacher_id，tmp1.cnt from（select max（tm p.cnt）作为tmpMax来自（选择teacher_id，count（teacher_id）作为来自课程g的cnt roup by teacher_id）as tmp）as tmp2，（select teacher_id，count（teacher_id）as cnt 从teacher_id的课程组）到tmp1，教师在哪里tmp1.cnt = tmp2.tmpMax 和teachers.teacher_id = tmp1.teacher_id;

我想出了上面的查询。是否有更简单的查询此问题？

Answer 1

这应该有效：

select teacher_name
from teachers
where teacher_id IN
(
    select t.teacher_id
    from teachers t inner join courses c on t.teacher_id = c.teacher_id
    group by t.teacher_id
    having count(*) = 
    (
        select max(courses_per_teacher) from
        (
            select teacher_id, count(*) as courses_per_teacher
            from teachers t inner join courses c on t.teacher_id = c.teacher_id
            group by teacher_id
        )
    )
)

伪代码中的逻辑：

找到ID在其中的教师姓名 - ＆gt;
课程数量为 - >的教师组。
等于 - >的最大数量
每位教师的课程数量列表

希望有所帮助。

Answer 2

SELECT teacher_id，teacher_name，COUNT（1）AS course_count
来自老师 WHERE course_count =（SELECT MAX（COUNT（1））FROM课程GROUP BY teacher_id）
GROUP BY teacher_id

Answer 3

试一试：

select a.teacher_name as 'Teacher', count(b.course_id) as 'Num of Courses'
from teachers a
inner join courses b on a.teacher_id = b.teacher_id
group by b.teacher_id
order by count(b.course_id) desc

修改的以下内容将为您提供与查询完全相同的结果：

select a.teacher_name as 'Teacher', a.teacher_id as 'Teacher Id', count(b.course_id) as 'Num of Courses' 
from teachers a 
inner join courses b on a.teacher_id = b.teacher_id 
group by b.teacher_id 
order by count(b.course_id) desc 
limit 1

Mysql Max查询

3 个答案: