『1』对查询结果进行排序（默认是按照Asc排序方式排序）
select * from employee order by age;
『2』对查询结果进行Eesc排序
select * from employee order by age desc;
『3』多次排序
select * from employee order by d_id asc,age asc;
『4』order by和group_concat函数连用
select sex,group_concat(name) from employee group by sex;
『5』GROUP BY 关键字与COUNT()函数连用
select sex,count(sex) from employee group by sex;
『6』GROUP BY关键与HAVING一起使用
select sex,count(sex) from employee group by sex having count(sex)>=3;
『7』GROUP BY 关键字与WITH ROLLUP一起使用
select sex,count(sex) from employee group by sex with rollup; （在输出最后一行做数据统计）
『8』LIMIT关键字
select * from employee limit 0,3;（从0开始一共3行）
