sql - 如何连接两个表但只返回匹配的行

Question

我有两个表，一个属性表和一个买家表，我正在尝试编写一个选择脚本，该脚本将显示一个属性列表，这些属性的房间数与指定客户所需的房间数相同。

我认为我需要使用内部联接来提取我需要的数据，但由于我对此仍然陌生，所以我有点困惑。我写的选择脚本如下，

SELECT DISTINCT Buyer.Buyer_Surname, Buyer.Rooms_Needed, Property.Property_Address as Property_for_sale, Property.Num_Rooms as Property_No_of_Rooms
FROM Buyer
INNER JOIN Property 
ON Property.Buyer_ID = Buyer.Buyer_ID
WHERE Buyer.Rooms_Needed = '5'
AND Property.Num_Rooms = '5'
AND Buyer.Buyer_ID = '70000';

然而，它告诉我没有选择任何行，但我知道有一个买家需要 5 间卧室，并且数据库中有 3 处特性有 5 间卧室。

这是我的表格；

CREATE TABLE Buyer 
(
Buyer_ID varchar(5) NULL,                           
Viewing_Data varchar2(50),                          
Maximum_Budget varchar2(50),                        
Purchase_Price varchar2(50),                        
Purchase_Date DATE,                                 
Buyer_Forename varchar2(50),                        
Buyer_Surname varchar2(50),                         
Buyer_Address varchar2(50),                         
Buyer_Town varchar2(50),                            
Buyer_Postcode varchar2(10),
Rooms_Needed varchar2(10),
Seller_ID Varchar2(5),
Staff_ID varchar2(5),
PRIMARY KEY (Buyer_ID),
FOREIGN KEY (Staff_ID) REFERENCES Staff(Staff_ID),
FOREIGN KEY (Seller_ID) REFERENCES Seller(Seller_ID)
); 

CREATE TABLE Property 
(
Property_ID varchar(5),                              
Property_Address varchar(25),
Property_Town varchar(25),
Property_Postcode varchar(25),                       
Asking_Price varchar2(20),                           
Date_Registered DATE,                                
Property_Type varchar2(50),                          
Num_Rooms varchar2(50),                              
Buyer_ID varchar(5),                                 
Seller_ID varchar(5),                                
Branch_ID varchar(5),                                
PRIMARY KEY (Property_ID),                           
FOREIGN KEY (Buyer_ID) REFERENCES Buyer(Buyer_ID),
FOREIGN KEY (Seller_ID) REFERENCES Seller(Seller_ID),
FOREIGN KEY (Branch_ID) REFERENCES Branch(Branch_ID)
);

Answer 1

您正在选择买家和属性(property) ID。如果这些排列一致，你会很幸运，但你的结果仍然不正确。要加入房屋拥有买家想要的房间数量的表，您需要加入房间数量:

SELECT DISTINCT Buyer.Buyer_Surname, Buyer.Rooms_Needed, 
    Property.Property_Address as Property_for_sale, Property.Num_Rooms as   
    Property_No_of_Rooms
    FROM Buyer
    INNER JOIN Property 
    ON Buyer.Rooms_Needed = Property.Num_Rooms;

如果需要按房间数过滤，还可以在末尾附加 WHERE:

... WHERE Buyer.Rooms_Needed = 5;