Sql學(xué)習(xí)第一天——SQL 練習(xí)題(建表/sql語句)_Mssql數(shù)據(jù)庫(kù)教程

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with ties一般是和Top , order by相結(jié)合使用的,會(huì)查詢出最后一條數(shù)據(jù)額外的返回值，接下來將為大家詳細(xì)介紹下，感興趣的各位可以參考下哈

題目:來自Madrid且訂單數(shù)少于3的消費(fèi)者

建表:

復(fù)制代碼代碼如下:www.zhaotila.cn

set nocount on --當(dāng) SET NOCOUNT 為 ON 時(shí)，不返回計(jì)數(shù)（表示受 Transact-SQL 語句影響的行數(shù)）。當(dāng) SET NOCOUNT 為 OFF 時(shí)，返回計(jì)數(shù)
use SY
GO
if object_Id('dbo.Orders') is not null
drop table dbo.Orders
GO
if object_Id('dbo.Customers') is not null
drop table dbo.Customers
GO
create table dbo.Customers
(
customerid char(5) not null primary key ,
city varchar(10) not null
);
insert into dbo.Customers values('FISSA','Madrid');
insert into dbo.Customers values('FRNDO','Madrid');
insert into dbo.Customers values('KRLOS','Madrid');
insert into dbo.Customers values('MRPHS','Zion');

create table dbo.Orders
(
orderid int not null primary key ,
customerid char(5) null references customers(customerid)
)
insert into dbo.Orders values(1,'FRNDO');
insert into dbo.Orders values(2,'FRNDO');
insert into dbo.Orders values(3,'KRLOS');
insert into dbo.Orders values(4,'KRLOS');
insert into dbo.Orders values(5,'KRLOS');
insert into dbo.Orders values(6,'MRPHS');
insert into dbo.Orders values(7,null);

------------------------------------------------------------------------------------------------------------------------------

做題分析：

復(fù)制代碼代碼如下:www.zhaotila.cn

 
select customerid as 消費(fèi)者,count(customerid) as 訂單數(shù) 
from dbo.Orders 
where customerid in ( 
select customerid 
from dbo.Customers 
where city = 'Madrid') 
group by customerid 
having count(customerid) < 3 

結(jié)果如圖所示：

--第一次想到的答案,突然發(fā)現(xiàn)少了一個(gè)來自Madrid的FISSA訂單,FISSA訂單數(shù)量為0,所以在Orders表中沒有出現(xiàn),所以上面的寫法會(huì)少一個(gè).

--推翻了上面的答案,又想到了用表的連接,而用內(nèi)連接出現(xiàn)的情況會(huì)和上面的一樣,所以我選擇了左連接,如下:

復(fù)制代碼代碼如下:www.zhaotila.cn

 
select C.customerid as 消費(fèi)者,count(O.customerid) as 訂單數(shù) 
from dbo.Customers as C left join dbo.Orders as O on C.customerid = O.customerid 
where C.city= 'Madrid' 
group by C.customerid 
having count(C.customerid) < 3 

結(jié)果如圖所示：

--查詢發(fā)現(xiàn)是正確的。

--分析查看不帶條件的左連接

復(fù)制代碼代碼如下:www.zhaotila.cn

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

復(fù)制代碼代碼如下:www.zhaotila.cn

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

結(jié)果如圖所示：

--書中給的標(biāo)準(zhǔn)答案是：

復(fù)制代碼代碼如下:www.zhaotila.cn

 
select C.customerid , count(O.orderid) as numorders 
from dbo.Customers as C left join dbo.Orders as O on C.customerid = O.customerid 
where C.city= 'Madrid' 
group by C.customerid 
having count(O.orderid) < 3 
order by numorders 

結(jié)果如圖所示：

--書中給的只是多了一個(gè)order by 進(jìn)行定義了排序方式(以numorders這一列的升序進(jìn)行排序)

分享：Sql學(xué)習(xí)第二天——SQL DML與CTE概述
關(guān)于DML即數(shù)據(jù)操縱語言；關(guān)于CTE即公用表表達(dá)式，接下來為大家介紹下CTE使用的地方以及優(yōu)點(diǎn)同時(shí)提供一個(gè)簡(jiǎn)單的CTE例題，感興趣的各位可以參考下哈

來源：模板無憂/所屬分類：Mssql數(shù)據(jù)庫(kù)教程/更新時(shí)間：2013-04-23

Sql學(xué)習(xí)第一天——SQL 練習(xí)題(建表/sql語句)_Mssql數(shù)據(jù)庫(kù)教程

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