查询各个部门的详细信息以及部门人数、部门平均工资Sql怎么写

要查询各个部门的详细信息以及部门人数、部门平均工资，可以使用以下SQL语句：

SELECT department.department_id, department.department_name, COUNT(employee.employee_id) AS department_size, AVG(employee.salary) AS average_salary FROM department INNER JOIN employee ON department.department_id = employee.department_id GROUP BY department.department_id, department.department_name