SQL 查询各个部门详细信息、人数和平均工资 - 代码示例与解释

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：\n\nsql\nSELECT \n department.department_id,\n department.department_name,\n COUNT(employee.employee_id) AS total_employees,\n AVG(employee.salary) AS average_salary\nFROM \n department\nLEFT JOIN \n employee ON department.department_id = employee.department_id\nGROUP BY \n department.department_id, department.department_name\n\n\n解释：\n1. 使用SELECT语句选择需要查询的字段：department.department_id（部门ID）、department.department_name（部门名称）、COUNT(employee.employee_id)（部门人数）、AVG(employee.salary)（部门平均工资）。\n2. 使用FROM语句指定查询的表为department。\n3. 使用LEFT JOIN语句连接employee表，条件为department.department_id = employee.department_id，这样可以将员工表与部门表关联起来。\n4. 使用GROUP BY语句按照department.department_id和department.department_name对结果进行分组。\n5. 最后得到每个部门的详细信息，包括部门人数和部门平均工资。