LintCode MySQL 1932/1933. 挂科最多的同学 I / II

-- Write your SQL Query here --
-- example: SELECT * FROM XX_TABLE WHERE XXX --
select student_id from
(
    select sum(if(is_pass=0, 1, 0)) ct, student_id 
    from exams
    group by student_id
    having ct > 0
    order by ct desc
    limit 1
) t

-- Write your SQL Query here --
-- example: SELECT * FROM XX_TABLE WHERE XXX --
select student_id from 
(
    select sum(if(is_pass=0, 1, 0)) ct, student_id 
    from exams
    group by student_id
    having ct > 0
) t2
where ct in 
(select max(ct) from 
    (
        select sum(if(is_pass=0, 1, 0)) ct, student_id 
        from exams
        group by student_id
        having ct > 0
    )t2
)