Mysql8.0习题系列（五）：子查询（一篇搞懂子查询做题技巧，超详细）

Mysql8.0习题系列

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文章目录

• Mysql8.0习题系列
• 子查询
• 1.查询和Zlotkey相同部门的员工姓名和工资
• 2.查询工资比公司平均工资高的员工的员工号，姓名和工资。
• 3.选择工资大于所有JOB_ID = 'SA_MAN'的员工的工资的员工的last_name, job_id, salary
• 4.查询和姓名中包含字母u的员工在相同部门的员工的员工号和姓名
• 5.查询在部门的location_id为1700的部门工作的员工的员工号
• 6.查询管理者是King的员工姓名和工资
• 7.查询工资最低的员工信息: last_name, salary
• 8.查询平均工资最低的部门信息
• 9.查询平均工资最低的部门信息和该部门的平均工资（相关子查询）
• 10.查询平均工资最高的 job 信息
• 11.查询平均工资高于公司平均工资的部门有哪些?
• 12.查询出公司中所有 manager 的详细信息
• 13.各个部门中 最高工资中最低的那个部门的 最低工资是多少?
• 14.查询平均工资最高的部门的 manager 的详细信息: last_name, department_id, email, salary
• 15. 查询部门的部门号，其中不包括job_id是"ST_CLERK"的部门号
• 16. 选择所有没有管理者的员工的last_name
• 17．查询员工号、姓名、雇用时间、工资，其中员工的管理者为 'De Haan'
• 18.查询各部门中工资比本部门平均工资高的员工的员工号, 姓名和工资（相关子查询）
• 19.查询每个部门下的部门人数大于 5 的部门名称（相关子查询）
• • 方法一
  • 方法二
• 20.查询每个国家下的部门个数大于 2 的国家编号（相关子查询）

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子查询

1.查询和Zlotkey相同部门的员工姓名和工资

首先我们查出Zlotkey所在的部门，再放入子查询中进行选择

SELECT last_name,salary
FROM employees
WHERE department_id = (SELECT department_id FROM employees
WHERE last_name = 'Zlotkey'
);

2.查询工资比公司平均工资高的员工的员工号，姓名和工资。

先找出平均工资

SELECT employee_id,last_name, salary
FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees);

3.选择工资大于所有JOB_ID = 'SA_MAN’的员工的工资的员工的last_name, job_id, salary

SELECT last_name, job_id, salary FROM employees
WHERE salary > (SELECT MAX(salary) FROM employees WHERE job_id	= 'SA_MAN');

4.查询和姓名中包含字母u的员工在相同部门的员工的员工号和姓名

SELECT employee_id, last_name
FROM employees
WHERE job_id IN (SELECT job_id FROM employees
WHERE last_name LIKE '%u%');

5.查询在部门的location_id为1700的部门工作的员工的员工号

SELECT 
  employee_id 
FROM
  employees 
WHERE department_id IN 
  (SELECT 
    department_id 
  FROM
  departments WHERE location_id = 1700);

6.查询管理者是King的员工姓名和工资

SELECT last_name, salary
FROM employees
WHERE manager_id IN
(SELECT employee_id FROM employees WHERE last_name = 'King'
);

7.查询工资最低的员工信息: last_name, salary

SELECT last_name, salary
FROM employees
WHERE salary = (SELECT MIN(salary) FROM employees);

8.查询平均工资最低的部门信息

SELECT * FROM departments
WHERE department_id = (SELECT department_id FROM employees GROUP BY department_id
ORDER BY AVG(salary) LIMIT 0,1);

9.查询平均工资最低的部门信息和该部门的平均工资（相关子查询）

SELECT d.*, avg_sl.avg_dep FROM departments d,(SELECT department_id, AVG(salary) avg_dep FROM employees GROUP BY department_id
ORDER BY AVG(salary)) avg_sl
WHERE d.`department_id` = avg_sl.department_id
LIMIT 1
;

10.查询平均工资最高的 job 信息

SELECT * FROM jobs WHERE job_id = (SELECT job_id FROM employees GROUP BY job_id
ORDER BY AVG(salary) LIMIT 1);

11.查询平均工资高于公司平均工资的部门有哪些?

SELECT department_id FROM employees
WHERE department_id IS NOT NULL
GROUP BY department_id
HAVING AVG(salary) > (SELECT AVG(salary) FROM employees);

12.查询出公司中所有 manager 的详细信息

SELECT * FROM employees WHERE employee_id 
IN (SELECT DISTINCT manager_id FROM employees);

13.各个部门中 最高工资中最低的那个部门的 最低工资是多少?

SELECT department_id, MAX(salary) FROM employees GROUP BY department_id
ORDER BY MAX(salary) ASC LIMIT 1;

14.查询平均工资最高的部门的 manager 的详细信息: last_name, department_id, email, salary

SELECT last_name, department_id, email,salary
FROM employees
WHERE manager_id = (SELECT DISTINCT employee_id FROM employees GROUP BY department_id ORDER BY AVG(salary) DESC 
LIMIT 1); 

15. 查询部门的部门号，其中不包括job_id是"ST_CLERK"的部门号

SELECT department_id
FROM departments d
WHERE department_id NOT IN (
SELECT DISTINCT department_id
FROM employees
WHERE job_id = 'ST_CLERK'
);

16. 选择所有没有管理者的员工的last_name

#方法1：
SELECT last_name 
FROM employees
WHERE employee_id = (SELECT employee_id FROM employees WHERE manager_id IS NULL);

SELECT last_name
FROM employees e1
WHERE NOT EXISTS (
SELECT *
FROM employees e2
WHERE e1.manager_id = e2.employee_id
);

17．查询员工号、姓名、雇用时间、工资，其中员工的管理者为 ‘De Haan’

SELECT employee_id, last_name, hire_date, salary
FROM employees
WHERE manager_id = (
SELECT employee_id FROM employees WHERE last_name = 'De Haan'
);

18.查询各部门中工资比本部门平均工资高的员工的员工号, 姓名和工资（相关子查询）

SELECT employee_id, last_name, salary 
FROM employees e, (SELECT department_id, AVG(salary) av_dep 
FROM employees GROUP BY department_id) e2
WHERE e.`department_id` = e2.department_id
AND e.`salary` > av_dep;

19.查询每个部门下的部门人数大于 5 的部门名称（相关子查询）

方法一

SELECT department_name
FROM departments
WHERE department_id
IN (SELECT department_id
FROM employees GROUP BY department_id
HAVING COUNT(*) > 5);

方法二

SELECT department_name,department_id
FROM departments d
WHERE 5 < (
SELECT COUNT(*)
FROM employees e
WHERE d.`department_id` = e.`department_id`
);

20.查询每个国家下的部门个数大于 2 的国家编号（相关子查询）

SELECT country_id
FROM locations l 
WHERE 2 <(
SELECT COUNT(*) FROM departments d
WHERE l.`location_id` = d.`location_id`);