insert into dbo.Orders values(4,'KRLOS');
group by customerid
--推翻了上面的答案,又想到了用表的连接,而用内连接出现的情况会和上面的一样,所以我选择了左连接,如下:
having count(customerid) < 3
group by C.customerid
GO
insert into dbo.Orders values(2,'FRNDO');
select C.customerid as 消费者,count(O.customerid) as 订单数

insert into dbo.Orders values(3,'KRLOS');

复制代码 代码如下:

customerid char(5) not null primary key ,

复制代码 代码如下:

insert into dbo.Orders values(1,'FRNDO');
select * from dbo.Customers as C left join dbo.Orders as O on C.customerid = O.customerid

--查询发现是正确的。
having count(C.customerid) < 3
create table dbo.Orders

where customerid in (
city varchar(10) not null

复制代码 代码如下:

insert into dbo.Customers values('KRLOS','Madrid');

GO
(
)

drop table dbo.Customers

题目:来自Madrid且订单数少于3的消费者

复制代码 代码如下:

select customerid as 消费者,count(customerid) as 订单数
GO
结果如图所示：

--第一次想到的答案,突然发现少了一个来自Madrid的FISSA订单,FISSA订单数量为0,所以在Orders表中没有出现,所以上面的写法会少一个.

select * from dbo.Customers as C left join dbo.Orders as O on C.customerid = O.customerid

结果如图所示：

use SY
--分析查看不带条件的左连接
where C.city= 'Madrid'
insert into dbo.Orders values(6,'MRPHS');
if object_Id('dbo.Orders') is not null
);
group by C.customerid

复制代码 代码如下:

from dbo.Customers as C left join dbo.Orders as O on C.customerid = O.customerid
order by numorders

orderid int not null primary key ,
select C.customerid , count(O.orderid) as numorders

insert into dbo.Customers values('FRNDO','Madrid');

--书中给的只是多了一个order by 进行定义了排序方式(以numorders这一列的升序进行排序)

--书中给的标准答案是：

select customerid
from dbo.Customers

create table dbo.Customers
结果如图所示：

from dbo.Orders

insert into dbo.Orders values(7,null);
结果如图所示：

drop table dbo.Orders
set nocount on --当 SET NOCOUNT 为 ON 时，不返回计数（表示受 Transact-SQL 语句影响的行数）。当 SET NOCOUNT 为 OFF 时，返回计数
from dbo.Customers as C left join dbo.Orders as O on C.customerid = O.customerid
where C.city= 'Madrid'

建表:

insert into dbo.Orders values(5,'KRLOS');

复制代码 代码如下:

做题分析：

insert into dbo.Customers values('MRPHS','Zion');
------------------------------------------------------------------------------------------------------------------------------

insert into dbo.Customers values('FISSA','Madrid');
if object_Id('dbo.Customers') is not null
where city = 'Madrid')
(
customerid char(5) null references customers(customerid)
having count(O.orderid) < 3