w3resource_MySQL练习：Subquery

w3resource_MySQL练习题：Subquery

1. Write a query to find the name (first_name, last_name) and the salary of the employees who have a higher salary than the employee whose last_name='Bull'

Sample table: employees

-- 要点：where里select
select first_name, last_name, salary
from employees
where salary>(
select salary from employees where last_name='Bull'
)

　

2. Write a query to find the name (first_name, last_name) of all employees who works in the IT department

Sample table: employees

-- 要点：直接where筛选
select first_name, last_name
from employees
where department_id='it'

3. Write a query to find the name (first_name, last_name) of the employees who have a manager and worked in a USA based department

Hint : Write single-row and multiple-row subqueries

Sample table: employees

Sample table: departments

Sample table: locations

-- 要点：多层嵌套查询
select first_name, last_name
from employees
where manager_id in (   -- 通过employees表获得manager_id
    select employee_id FROM employees
    where department_id in (  -- 通过departments表获得在USA的department_id
        select department_id from departments
        where location_id in (  -- 通过locations表获得在USA的location_id
            select location_id from locations
            where country_id='US'
        )
    )
)

4. Write a query to find the name (first_name, last_name) of the employees who are managers

Sample table: employees

-- 要点：在where中传入manager_id
select first_name, last_name
from employees
where employee_id in (
　　select distinct manager_id from employees
)

　　

5. Write a query to find the name (first_name, last_name), and salary of the employees whose salary is greater than the average salary

Sample table: employees

-- 要点：where
select first_name, last_name, salary
from employees
where salary>(
    select avg(salary) from employees
)

6. Write a query to find the name (first_name, last_name), and salary of the employees whose salary is equal to the minimum salary for their job grade

Sample table: employees

Sample table: jobs

-- 方法1：使用where嵌套查询
select e.first_name, e.last_name, e.salary
from employees as e
where e.salary=(
    select j.min_salary from jobs as j where j.job_id=e.job_id
)
-- 方法2：使用多表连接（from连接多张表）
select e.first_name, e.last_name, e.salary
from employees as e, jobs as j
where j.job_id=e.job_id
and e.salary=j.min_salary

 

7. Write a query to find the name (first_name, last_name), and salary of the employees who earns more than the average salary and works in any of the IT departments

Sample table: employees

Sample table: departments

-- 要点：where
select first_name, last_name, salary
from employees
where salary>(avg salary from employees)
and department_id in (select distinct department_id from departments where department_name like 'IT%')

8. Write a query to find the name (first_name, last_name), and salary of the employees who earns more than the earning of Mr. Bell

Sample table: employees

Sample table: departments

-- 要点：where
select first_name, last_name, salary
from employees
where salary>(select salary from employees where last_name='Bell')

 

9. Write a query to find the name (first_name, last_name), and salary of the employees who earn the same salary as the minimum salary for all departments

Sample table: employees

Sample table: departments

-- 要点：where + min()
select first_name, last_name, salary
from employees
where salary=(select min(salary) from employees)

 

10. Write a query to find the name (first_name, last_name), and salary of the employees whose salary is greater than the average salary of all departments

Sample table: employees

-- 要点：where + min()
select first_name, last_name, salary
from employees
where salary>(select avg(salary) from employees)

11. Write a query to find the name (first_name, last_name) and salary of the employees who earn a salary that is higher than the salary of all the Shipping Clerk (JOB_ID = 'SH_CLERK'). Sort the results of the salary of the lowest to highest

Sample table: employees

-- 要点：where
select first_name, last_name, salary
from employees
where salary>(
    select max(salary) from employees where job_id='SH_CLERK'
)
order by salary asc

12. Write a query to find the name (first_name, last_name) of the employees who are not supervisors

Sample table: employees

-- 要点：where + not in
select first_name, last_name
from employees
where employee_id not in (
    select manager_id from employees
)

13. Write a query to display the employee ID, first name, last name, and department names of all employees

Sample table: employees

Sample table: departments

-- 1. 多表连接
select employee_id, first_name, last_name, department_name
from employees, departments
where employees.department_id=departments.department_id
-- 2. select内筛选
SELECT employee_id, first_name, last_name,
(SELECT department_name FROM departments d
WHERE e.department_id = d.department_id) department
FROM employees e ORDER BY department;

14. Write a query to display the employee ID, first name, last name, salary of all employees whose salary is above average for their departments

Sample table: employees

Sample table: departments

-- 要点：where
select employee_id, first_name, last_name, salary
from employees e
where salary>(
    select avg(salary) from employees e2 where e1.department_id = e2.department_id
)

15. Write a query to fetch even numbered records from employees table

Sample table: employees

-- 要点：判断奇偶数，使用%2进行取余
select *
from employees
where (employee_id%2<>0)

16. Write a query to find the 5th maximum salary in the employees table

Sample table: employees

-- 1. 首先按salary进行降序排列取前五行，然后顺序排列取第一行
select *
from (select * from employees order by salary desc limit 5)
order by salary
limit 1
-- 2. where内做筛选
SELECT DISTINCT salary
FROM employees e1
WHERE 5 = (
    SELECT COUNT(DISTINCT salary)
    FROM employees e2
    WHERE e2.salary >= e1.salary
);

17. Write a query to find the 4th minimum salary in the employees table

Sample table: employees

-- 1. 首先按salary进行排列取前四行，然后顺序排列取第一行
select *
from (select * from employees order by salary asc limit 4)
order by salary
limit 1
-- 2. where内做筛选
SELECT DISTINCT salary
FROM employees e1
WHERE 4 = (
    SELECT COUNT(DISTINCT salary)
    FROM employees e2
    WHERE e2.salary >= e1.salary
);

18. Write a query to select last 10 records from a table

Sample table: employees

-- 要点：根据employee_id进行排序
select *
from employees
order by employee_id desc
limit 10

19. Write a query to list the department ID and name of all the departments where no employee is working

Sample table: employees

Sample table: departments

-- 要点：通过department_id进行判断
select department_id, department_name
from departments
where department_id not in (
select distinct department_id from employees
)

20. Write a query to get 3 maximum salaries

Sample table: employees

-- 要点：limit
select *
from employees
order by salary desc
limit 3

21. Write a query to get 3 minimum salaries

Sample table: employees

-- 要点：limit
select *
from employees
order by salary asc
limit 3

22. Write a query to get nth max salaries of employees

Sample table: employees

-- 要点：limit a, b 取数范围为：第[a+1, a+b]条记录
select *
from employees
order by salary
limit (n-1), 1