Leetcode SQL (#1613, #1623, #1633)

select a.id as ids
from (
    select 1 as id union
    select 2 as id union
    select 3 as id union
    select 4 as id union
    select 5 as id union
    select 6 as id union
    select 7 as id union
    select 8 as id union
    select 9 as id union
    select 10 as id union
    select 11 as id union
    select 12 as id union
    select 13 as id union
    select 14 as id union
    select 15 as id union
    select 16 as id union
    select 17 as id union
    select 18 as id union
    select 19 as id union
    select 20 as id union
    select 21 as id union
    select 22 as id union
    select 23 as id union
    select 24 as id union
    select 25 as id union
    select 26 as id union
    select 27 as id union
    select 28 as id union
    select 29 as id union
    select 30 as id union
    select 31 as id union
    select 32 as id union
    select 33 as id union
    select 34 as id union
    select 35 as id union
    select 36 as id union
    select 37 as id union
    select 38 as id union
    select 39 as id union
    select 40 as id union
    select 41 as id union
    select 42 as id union
    select 43 as id union
    select 44 as id union
    select 45 as id union
    select 46 as id union
    select 47 as id union
    select 48 as id union
    select 49 as id union
    select 50 as id union
    select 51 as id union
    select 52 as id union
    select 53 as id union
    select 54 as id union
    select 55 as id union
    select 56 as id union
    select 57 as id union
    select 58 as id union
    select 59 as id union
    select 60 as id union
    select 61 as id union
    select 62 as id union
    select 63 as id union
    select 64 as id union
    select 65 as id union
    select 66 as id union
    select 67 as id union
    select 68 as id union
    select 69 as id union
    select 70 as id union
    select 71 as id union
    select 72 as id union
    select 73 as id union
    select 74 as id union
    select 75 as id union
    select 76 as id union
    select 77 as id union
    select 78 as id union
    select 79 as id union
    select 80 as id union
    select 81 as id union
    select 82 as id union
    select 83 as id union
    select 84 as id union
    select 85 as id union
    select 86 as id union
    select 87 as id union
    select 88 as id union
    select 89 as id union
    select 90 as id union
    select 91 as id union
    select 92 as id union
    select 93 as id union
    select 94 as id union
    select 95 as id union
    select 96 as id union
    select 97 as id union
    select 98 as id union
    select 99 as id union
    select 100 as id 
) a
left join Customers c 
    on a.id = c.customer_id
where (
    c.customer_id is null
    and a.id <= (select max(customer_id) from Customers)
    )
order by 1

select 
a.student_name as member_A,
b.student_name as member_B,
c.student_name as member_C
from SchoolA a
    cross join SchoolB b
    cross join SchoolC c
where
a.student_name <> b.student_name
and b.student_name <> c.student_name
and a.student_name <> c.student_name
and a.student_id <> b.student_id
and b.student_id <> c.student_id
and a.student_id <> c.student_id

select 
r.contest_id, 
round((count(distinct r.user_id) / u.users) *100,2) as percentage
from Register r
    join (
        select 
        count(distinct user_id) as users 
        from Users
    ) u 
        on 1=1
group by 1
order by 2 desc, 1