1.普通查询
select * from info; #查询所有内容
select Code,Name from Info #查询某几列
2.条件查询
select * from Info where Code='p001' #条件查询
select * from Info where Nation ='n001' and Sex= true #条件之间并的关系
select * from Info where Nation = 'n001' and sex = '1'
select * from Info where Sex = false or Nation = 'n002'#条件之间或者的关系
3.模糊查询（搜索关键字）
select * from Chinastates where areaname like '中%' #查询以中开头的
select * from Chinastates where Areaname like '%城%' #查询包含 城的信息
select * from Chinastates where Areaname like '_城%' #查询城 在第二个位置出现的数据
4.排序
select * from Car order by Code desc #desc降序 asc升序
select * from Car order by Brand
select * from Car order by Brand,Powers #按照两个列排序
5.统计查询（聚合函数）
select count(*) from Car #查询总条数 * 代表所有列
select count(Code) from Car #查询某一列
select max(Price) from Car #查询 price列里的最大值
select min(price) from Car #查询最小值
select avg(price) from Car #查询平均值
select sum(price) from Car #查询总和
6.分组查询
select Brand,count(*) from Car group by Brand #根据系列(Brand)分组(group)查看每组的数据条数
select Code,Brand,count(*) from Car group by Brand #根据Brand分组查看Code，Brand的数据条
select * from Car group by Brand having count(*) >2 #查询分组之后数据条数大于2的,group后面不能加 where
7.分页查询
select * from Car limit 0,5 #查询跳过0条 取5条
select * from Car limit 5,5 #跳过几条取几条数据