按表达式或函数分组：

#案例：按员工的姓名的长度分组，查询每一组的员工个数，筛选员工个数大于五

SELECTCOUNT(*),LENGTH(last_name)FROMemployeesGROUP BYLENGTH(last_name)HAVINGCOUNT(*)>5;

按多个字段分组：
#案例：查询每个部门每个工种的员工的平均工资

SELECT AVG(salary),department_id,job_idFROMemployeesGROUP BYdepartment_id,job_id;

排序
#案例：查询每个部门每个工种的部门编号不为null的员工的平均工资>10000，并且按平均工资的高低显示

SELECTAVG(salary),department_id,job_idFROMemployeesWHEREdepartment_id IS NOT NULLGROUP BYdepartment_id,job_idHAVINGAVG(salary)>10000ORDER BYAVG(salary) DESC;