I need help with a MySQL query - mysql

Question

I have two tables - `employee` and `department`.
1. `employee` table contains column id,employee name and dept_id
2. `department` table contains column id, department name.
I need exact department name which contains
1. maximum employee and
2. no employee
Edited:
Apologizing for bad grammar, here is the example for above two questions what i need.
1. for eg: if two department contains same number of employees, i need to show both department not single by limit.
2. for eg: if more than one department contains 0 employees, i must show those departments particularly.

Answer 1

select department_name as `department name`,
count(*) as `number of employees`
from employee
inner join department
on employee.dept_id = department.id
group by department_name
order by count(*) desc
limit 1
i think that should do it. i've not done anything with mysql in a while.
edit: missed the second question
select department_name as `department name`,
count(*) as `number of employees`
from employee
left join department
on employee.dept_id = department.id
group by department_name
HAVING count(*) = 0

Answer 2

Answer to the first question:
WITH epcount(dept_id, ep_count) AS
(
SELECT dept_id, COUNT(*) AS ep_count
FROM employee
GROUP BY dept_id
)
SELECT d.name FROM epcount AS ec1 JOIN department AS d ON ec1.dept_id=d.id
WHERE NOT EXISTS
(SELECT * FROM epcount AS ec2 WHERE ec1.ep_count < ec2.ep_count)
Answer to the second question:
SELECT name FROM department AS d
WHERE NOT EXISTS
(SELECT * FROM employee AS e WHERE d.id=e.dept_id)

Answer 3

If I read the question right, you need:
select department_name,
count(employee.dept_id) as num_employees
from department
left join employee on employee.dept_id = department.id
group by department_name
having count(employee.dept_id) = 0 or
count(employee.dept_id) = (select count(dept_id)
from employee
group by employee.id
order by count(dept_id) desc
limit 1)

Answer 4

This will get you a sorted list of departments, sorted by number of employees.
SELECT `dept`.`id`, `dept`.`name`, COUNT(`employee`.`id`) as `employee_count`
FROM `dept` LEFT JOIN `employee`
ON `employee`.`dept_id` = `dept`.`id`
GROUP BY `dept`.`id`
ORDER BY `employee_count`
To get departments with no employees, add:
AND `employee_count` = 0
...before the GROUP BY.
To get the department with the most employees, add DESC LIMIT 1 to the end.

Answer 5

Query that shows department names with maximum employees and number of employees in it:
SELECT department.name, COUNT(employee.name) from department
INNER JOIN employee
ON employee.dept_id = department.id
GROUP BY department.name
ORDER BY COUNT(employee.name) DESC limit 1
Query that shows departments with no employees:
SELECT department.name from department
LEFT JOIN employee
ON employee.dept_id = department.id
HAVING COUNT(employee.name) = 0
GROUP BY department.name
If you need to show it in one query, paste first query, add UNION ALL and then paste second query.