数据库————Select 查询

--创建mydb数据库
create database mydb
go
--使用数据库
use mydb
go
--水果表
create table Fruit
(
Ids varchar(50) primary key,
[Name] varchar(50) not null,
Price decimal(8,2),
Source varchar(50),
Numbers int,    --库存数量
[Image] varchar(50)
)
go
--向表中添加数据
insert into fruit values('k001','苹果',2.4,'烟台',100,'image/0.gif')
insert into fruit values('k002','菠萝',1.4,'广东',100,'image/1.gif')
insert into fruit values('k003','桔子',2.4,'福州',100,'image/2.gif')
insert into fruit values('k004','葡萄',2.4,'新缰',100,'image/3.gif')
insert into fruit values('k005','樱桃',2.4,'青岛',100,'image/4.gif')
insert into fruit values('k006','桃子',2.4,'花果山',100,'image/5.gif')
insert into fruit values('k007','香蕉',2.4,'济南',100,'image/6.gif')

--用户表
create table Login
(
UserName varchar(50) primary key,    --用户名
[Name] varchar(50),    --真实姓名
Password varchar(50),    --密码
Account decimal(18,2)    --账户余额
)
go
insert into login values('zhangsan','张三','666666',50)
insert into login values('lisi','李四','666666',50)
insert into login values('wangwu','王五','666666',50)

--订单表
create table Orders
(
Code varchar(50) primary key,    --以“用户名yyyyMMddhhmmssms”的形式作主键
UserName varchar(50) references Login(Username),    --订购人员代号作外键
OrderTime datetime,    --订购时间
)
go

--订单内容表
create table OrderDetails
(
Ids int identity primary key,
OrderCode varchar(50) references Orders(Code),--订单号
FruitCode varchar(50) references Fruit(Ids),--水果代号
[Count] int ,    --水果的个数
)
go

select * from fruit
select * from login
select * from orders
select * from orderdetails

--查询
select * from Fruit --查所有
select Name,Source from Fruit --查特定列

select Ids '代号',Name '名称',Price '价格',Source '产地' from Fruit -- 修改列名

select * from Fruit where Ids='K006'
select * from Fruit where Price=2.4 and Source='烟台' -- 查指定行按条件查

select * from Fruit where Price between 2.0 and 4.0 --查指定行按范围查

select * from Fruit where Numbers in (90,80,70)--查指定行，离散查

select distinct Numbers from Fruit --去重查询

select * from News

select * from News where title like '%户口' --模糊查询，查以户口结尾的
select * from News where title like '大熊猫%' --模糊查询，查以大熊猫开头的
select * from News where title like '%大熊猫%' --模糊查询，查以包含大熊猫的
select * from News where title like '%外币货_'--模糊查询，查外币货之后只有一个字符的

select * from Fruit order by Numbers asc --按照Numbers列升序排，如果不加asc默认以升序排
select * from Fruit order by Numbers desc --按照Numbers列降序排
select * from Fruit order by Numbers,Price --先按照Numbers排，然后再按照Price排

select COUNT(*) from Fruit --返回Fruit表里面有多少条数据
select AVG(Numbers)from Fruit --返回某一列的平均值
select SUM(Numbers) from Fruit --返回某一列的所有数据和
select MAX(Numbers) from Fruit --返回某一列中的最大值
select MIN(Numbers) from Fruit --返回某一列中的最小值

select *,(Price*0.8) as '折后价格' from Fruit --加一列数据库中没有的列，这里是加了8折后的价格列

select Numbers, COUNT(*) from Fruit group by Numbers --根据某一列分组，求出该组内成员的个数
select Numbers, COUNT(*) from Fruit group by Numbers having COUNT(*)>1--根据某一列分组，求出该组内成员的个数,返回成员个数大于1的

%----代表任意多个字符
‘%户口’---以户口结尾，户口前有多个字符
‘户口%’----以户口开头，户口后面有多个字符
'%户口%'----包含户口，户口前后有多个字符

‘%外币货_’----外币货后面只有一个字符，之前有多个字符

like----模糊查询
distinct---去除重复