导入导出数据
把表变成sql代码
备份与还原
增，删，改，查 CRUD
#添加：
insert into <表名>[(列1,列2....)] values(<'值1'>[,'值2'])
注意：
1.列与值要匹配（数量，类型，次序）
2.列可以省掉，但值必须与表中的总列数和列的次序完全对应。
3.自增长列，不能省掉自增列，给自增列赋个''
#删
delete from car 不同于 drop table xx
delete from car where code='c001'
delete from car where brand='b001' or brand='b004'
delete from car where brand='b001' || brand='b004'
delete from car where brand='b007' && price>50
delete from car where brand='b007' and price>50
<> !=
#修改
update <表名> set <列=值>[,列=值...] where .....
update car set brand='b008' where code='c001' or code='c002';
update car set name='奔驰', brand='b009', time='2016-2-2' where code='c002'
update car set price=price*0.9
update car set price=price*0.95 where price>30
update car set price=price*0.1 where (brand='b002' or brand='b003')&&price>40
#查询
一、简单查询
select * from 表名
select 列名1,列名2... from 表名 --投影
select * from 表名 where 条件 --筛选
select Code as '代号',Name as '姓名' from Info
1.等值与不等值
select * from car where code='c001';
select * from car where code != 'c001';
select * from car where price > 30;
--下面的都是范围
select * from car where price >=30 && price <=50;
select * from car where price between 30 and 50
select * from car where brand='b002' || brand='b004' || brand='b006'
select * from car where brand in ('b002','b004','b006')
2.模糊查
select * from car where name like '宝马%' %--任意多个任意字符 #查找以宝马开头的
select * from car where name like '%5%' #查找包含5的
select * from car where name like '%型' #查找以型结尾的
select * from car where name like '__5%' _ -- 一个任意字符 #查找第三个字符是5的行
select * from car where name like'__5' #查找第三个字符是5并且总长度就是三个字符
3.排序
select * from 表名 where .... order by 列名 [ASC/DESC],列名[asc/desc]....
select * from car order by price desc
select * from car order by brand desc,price asc
select * from car where brand in('b002','b004','b006') order by brand asc,price desc #先找出来再排序
4.范围查询
select * from Car where Price>=40 and Price<=60
select * from Car where Price between 40 and 50
5.聚合函数，统计查询
select sum(Price) from Car #查询所有价格之和 sum()求和
select count(Code) from Car #查询数据条数
select max(Code) from Car #求最大值
select min(Brand) from Car #求最小值
select avg(Price) from Car #求平均值
6.分页查询
#每页显示5条数据，取第2页的数据
select * from Car limit (n-1)*5,5
7.去重查询
select distinct Brand from Car
8.分组查询
select count(*),Brand from Car group by Brand
select Brand as '系列号' from Car group by Brand having count(*)>3 #分组之后根据条件查询使用having 不使用where