下面的SQL语句纯属SQL语句，注释比较少，希望大家能明白只是做个简单的笔记
group by: select emp_id,city from employee_tbl group by city,emp_id;对返回数据city，在根据emp_id进行分组
select emp_id , sum(salary) from employee_pay_tbl group by salary, emp_id 返回emp_id salary字段的总和，然后根据薪水和雇员ID对数据分组
select sum(salary) as tottal_salary from employee_pay_tbl; 返回全部薪水的总和
select sum(salary) from employee_pay_tbl group by salary; 返回不同的薪水总和
select city ,count(*) from employee_tbl group by city ;不同城市的记录总数
select city , avg(pay_rate),avg(salary) fromemployee_pay_tbl group by city; 获得不同城市的平均小时工资和薪水
select city ,avg(pay_rate),avg(salary) from emp_pay_tmp where city in ('BEIJING','SHANGHAI') group by city order by 2,3返回BEIJINGSHANGHAI城市的平均小时和薪水，基于city进行分组 最后排序
select city , max(pay_rate) ,min (salary) from emp_pay_tmp group by city;
CUBE 和ROLLUP
rollup : group by rollup(order column list of grouping sets)
goup by order column list of grouping sets with rollp (mysql中)
双表查询
select city ,zip ,avg(pay_rate),avg(salary) from employee_tbl e inner joinemployee_pay_tbl p on e.emp_id=p,emp_id group by city , zip order by city , zip; 根据城市和邮编获得平均工资
select city zip,avg(pay_rate), avg(salary) fromemployee_tbl e inner joinemployee_pay_tbl p on e.emp_id =p.emp_id group by rollup(city,zip);使用rollup语句获取小计数据
CUBE ： select city ,zip , avg(pay_rate) ,avg(salary) fromemployee_tbl e inner joinemployee_pay_tbl p on e.emp_id = p.emp_id group by cube(city,zip);根据每种字段组合分别汇总
having: 位置
select
from
where
group by
having
order by
select city ,avg(pay_rate),avg(salary) from emp_pay_tmp where city <> 'GREENWOOD' group by city having avg(salary) >2000 order by 3;选择除了GREENWOOD之外的所有城市的平均小时工资和薪水，输出按照 分组， 显示超过2000的分组（城市）
