|580|[Count Student Number in Departments](https://leetcode.com/problems/count-student-number-in-departments/)|[Solution](../master/database/_580.sql) | || Medium | Left Join

|577|[Employee Bonus](https://leetcode.com/problems/employee-bonus/)|[Solution](../master/database/_577.sql)||| Easy|

|574|[Winning Candidate](https://leetcode.com/problems/winning-candidate/)|[Solution](../master/database/_574.sql)||| Medium|

|571|[Find Median Given Frequency of Numbers](https://leetcode.com/problems/find-median-given-frequency-of-numbers/)|[Solution](../master/database/_571.sql)||| Hard|

|570|[Managers with at Least 5 Direct Reports](https://leetcode.com/problems/managers-with-at-least-5-direct-reports/)|[Solution](../master/database/_570.sql)||| Medium|

|569|[Median Employee Salary](https://leetcode.com/problems/median-employee-salary/)|[Solution](../master/database/_569.sql)||| Hard|

|262|[Trips and Users](https://leetcode.com/problems/trips-and-users/)|[Solution](../master/database/_262.sql)||| Hard| Inner Join

select FORMAT(avg(n.Number),4)*1.0as median

from Numbers nleft join

(

selectNumber, @prev := @countas prevNumber, (@count := @count+ Frequency)as countNumber

from Numbers,

(select @count :=0, @prev :=0, @total := (selectsum(Frequency)from Numbers)) temporder byNumber

) n2

onn.Number=n2.Number

(prevNumber< floor((@total+1)/2)and countNumber>= floor((@total+1)/2))

(prevNumber< floor((@total+2)/2)and countNumber>= floor((@total+2)/2))