简单查询
1查询所有数据
selete * from info
2查询指定列
select code,name from info
3给列指定名称
select code as ‘代号‘，name as ‘姓名‘ from info
4条件查询
select * from info where code=‘p001‘
5模糊查询：根据关键字查询
select * from car where name like ‘_奥迪_‘ %百分号奥迪前面可以有N个字符，可以后面有N个字符；_下滑线只能出现一个字符，
6排序查询
select * from car order by price desc，oil desc
代表以价格进行排序,price后面不加，默认升序排列，降序使用desc；price是第一优先级排序，如果价格相等则oil排序
7去重查询
select distinct brand from car
8分页查询
select * from car limit 5，5
跳过几条，取几条
9统计查询或聚合函数
select count(*) from car查询出多少条数据
取最大值
select max(price) from car
取最小值
select min(price) from car
取平均值
select avg(price) from car
分组查询
select brand,count(*) from car group by brand
select brand from car group by brand having count(*)>=3
范围查询
select * from car where price>=40 and price<=60
select * from car where price between 40 and 60
离散查询
select * from car where price in(10,20,30,40)在里面出现
select * from car where price not in(10,20,30,40)不在里面出现
联合查询
union
连接查询
形成笛卡尔积
