我需要一個MySQL查詢

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 

編輯幫助：

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

回答第一個問題：

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) 

回答了第二個問題：

SELECT name FROM department AS d 
    WHERE NOT EXISTS 
     (SELECT * FROM employee AS e WHERE d.id=e.dept_id) 

Answer 2

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 

我認爲應該這樣做。我在一段時間內沒有對mysql做任何事情。

編輯：錯過了第二個問題

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 3

這將讓你的部門的排序列表，員工數量排序。

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` 

要獲得主管部門沒有員工，添加：

AND `employee_count` = 0 

...在GROUP BY之前。

要獲得員工人數最多的部門，請添加DESC LIMIT 1到最後。

Answer 4

查詢，顯示在它最大的員工和員工人數的部門名稱：

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 

查詢，顯示部門沒有員工：

SELECT department.name from department 
LEFT JOIN employee 
ON employee.dept_id = department.id 
HAVING COUNT(employee.name) = 0 
GROUP BY department.name 

如果你需要顯示它在一個查詢，粘貼第一個查詢，添加UNION ALL，然後粘貼第二個查詢。

Answer 5

如果我讀的問題的權利，你需要：

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)