1. 查询工资最低的员工信息: last_name, salary

①查询最低的工资

SELECT MIN(salary)
FROM employees

②查询last_name,salary，要求salary=①

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

2. 查询平均工资最低的部门信息

方式一：

①各部门的平均工资

SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id

②查询①结果上的最低平均工资

SELECT MIN(ag)
FROM (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
) ag_dep

③查询哪个部门的平均工资=②

SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary)=(
SELECT MIN(ag)
FROM (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
) ag_dep

);

④查询部门信息

SELECT d.*
FROM departments d
WHERE d.department_id=(
SELECT department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary)=(
SELECT MIN(ag)
FROM (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
) ag_dep

)

);

方式二：

①各部门的平均工资

SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id

②求出最低平均工资的部门编号

SELECT department_id
FROM employees
GROUP BY department_id
ORDER BY AVG(salary)
LIMIT 1;

③查询部门信息

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

3. 查询平均工资最低的部门信息和该部门的平均工资

①各部门的平均工资

SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id

②求出最低平均工资的部门编号

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

③查询部门信息

SELECT d.*,ag
FROM departments d
JOIN (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
ORDER BY AVG(salary)
LIMIT 1

) ag_dep
ON d.department_id=ag_dep.department_id;

4. 查询平均工资最高的 job 信息

①查询最高的job的平均工资

SELECT AVG(salary),job_id
FROM employees
GROUP BY job_id
ORDER BY AVG(salary) DESC
LIMIT 1

②查询job信息

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

);

5. 查询平均工资高于公司平均工资的部门有哪些?

①查询平均工资

SELECT AVG(salary)
FROM employees

②查询每个部门的平均工资

SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id

③筛选②结果集，满足平均工资>①

SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary)>(
SELECT AVG(salary)
FROM employees

);

6. 查询出公司中所有 manager 的详细信息.

①查询所有manager的员工编号

SELECT DISTINCT manager_id
FROM employees

②查询详细信息，满足employee_id=①

SELECT *
FROM employees
WHERE employee_id =ANY(
SELECT DISTINCT manager_id
FROM employees

);

7. 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

①查询各部门的最高工资中最低的部门编号

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

②查询①结果的那个部门的最低工资

SELECT MIN(salary) ,department_id
FROM employees
WHERE department_id=(
SELECT department_id
FROM employees
GROUP BY department_id
ORDER BY MAX(salary)
LIMIT 1

);

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

①查询平均工资最高的部门编号

SELECT
department_id
FROM
employees
GROUP BY department_id
ORDER BY AVG(salary) DESC
LIMIT 1

②将employees和departments连接查询，筛选条件是①

SELECT 
    last_name, d.department_id, email, salary 
FROM
    employees e 
    INNER JOIN departments d 
        ON d.manager_id = e.employee_id 
WHERE d.department_id = 
    (SELECT 
        department_id 
    FROM
        employees 
    GROUP BY department_id 
    ORDER BY AVG(salary) DESC 
    LIMIT 1) ;