简单查询笔记

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 Sex=false or Nation='n002' #条件之间或者的关系

3.模糊查询

 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.排序查询
 
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 括号里可以加code 耗时少


select max(Price) from Car#查询最大值
 

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

select max(price),min(price),avg(price) from car #如果要一起查的话只有这样
 
6.分组查询
 

select  price,count(*), max(price) from fruit group by price #根据系列分组查看每组的数据条数


select *from Car group by Brand having count(*)>2 #查询分组之后数据条数大于2的


7.分页查询
select *from Car limit 0,5  #跳过几条数据取几条数据 
 

8.去重查询

select distinct oil from car