MySQL 查询示例：薪资、部门和员工信息

查询薪资大于 1500 的工作岗位及其员工人数：

SELECT job_title, COUNT(*) AS employee_count
FROM employees
JOIN jobs ON employees.job_id = jobs.job_id
WHERE jobs.min_salary > 1500
GROUP BY job_title;

查询所有部门及其员工信息，包括无员工部门：

SELECT departments.department_name, employees.*
FROM departments
LEFT JOIN employees ON departments.department_id = employees.department_id;

查询部门编号、名称、位置和员工人数：

SELECT department_id, department_name, location_id, COUNT(*) AS employee_count
FROM employees
GROUP BY department_id, department_name, location_id;