1.注释语法：--，#

2.后缀是.sql的文件是数据库查询文件

3.保存查询

4.在数据库里面 列有个名字叫字段 行有个名字叫记录

CRUD操作：

create 创建(添加)

read 读取

update 修改

delete 删除

1、添加数据

insert into Info values('p009','张三',1,'n001','2016-8-30 12:9:8') ;

给特定的列添加数据

insert into Info (code,name) values('p010','李四');

自增长列的处理

insert into family values('','p001','数据','T001','数据',1);

insert into 表名 values(值)

2、删除数据

删除所有数据

delete from family

删除特定的数据

delete from Info where code='p001'

delete from 表名 where 条件

3、修改数据

修改所有数据

update Info set name='徐业鹏'

修改特定数据

update Info set name='吕永乐' where code='p002'

修改多列

update Info set name='吕永乐',sex=1 where code='p003'

update 表名 set 要修改的内容 where 条件

4、读取数据

(1)简单读取,查询所有列(*) 所有行(没有加条件)

select * from Info

(2)读取特定列

select code,name from Info

(3)条件查询

select * from Info where code='p003'

(4)多条件查询

select * from Info where code='p003' or nation='n002' #或的关系

select * from Info where sex=0 and nation='n002' #与的关系

(5)关键字查询(模糊查询)

查所有包含奥迪的汽车

select * from car where name like '%奥迪%'; #百分号%代表任意多个字符

查以'皇冠'开头的所有汽车

select * from car where name like '皇冠%';

查询汽车名称中第二个字符是'马'的

select * from car where name like '_马%'; #下划线_代表任意一个字符

(6)排序查询

select * from car order by powers #默认升序排列

select * from car order by powers desc #升序asc 降序 desc

先按brand升序排，再按照price降序排

select * from car order by brand,price desc

(7)范围查询

select * from car where price>40 and price<60

select * from car where price between 40 and 60

(8)离散查询

select * from car where price=30 or price=40 or price=50 or price=60;

select * from car where price in(30,40,50,60)

select * from car where price not in(30,40,50,60)

(9)聚合函数(统计查询)

select count(*) from car

select count(code) from car #取所有的数据条数

select sum(price) from car #求价格总和

select avg(price) from car #求价格的平均值

select max(price) from car #求最大值

select min(price) from car #求最小值

(10)分页查询

select * from car limit 0,10 #分页查询，跳过几条数据(0)取几条(10)

规定一个每页显示的条数：m

当前页数：n

select * from car limit (n-1)*m,m

(11)去重查询

select distinct brand from car

(12)分组查询

查询汽车表中，每个系列下汽车的数量

select brand,count(*) from car group by brand

分组之后，只能查询该列或聚合函数

取该系列价格平均值大于40的系列代号

select brand from car group by brand having avg(price)>40

取该系列油耗最大值大于8的系列代号

select brand from car group by brand having max(oil)>8