Mysql 简明教程
MySQL - Right Join
MySQL Right Join
The Right Join or Right Outer Join query in MySQL returns all rows from the right table, even if there are no matches in the left table. So, if zero records are matched in the left table, the right join will still return a row in the result, but with a NULL value in each column of the left table.
In short, a right join returns all the values from the right table, plus matched values from the left table or NULL in case of no matching join predicate.
The resultant table displayed after implementing the Right Join is not stored anywhere in the database.
Syntax
以下是 SQL 中右侧连接的基本语法：
SELECT table1.column1, table2.column2...
FROM table1
RIGHT JOIN table2
ON table1.common_field = table2.common_field;Example
假设我们正在创建一个名为 CUSTOMERS 的表格，其中包含客户的个人详细信息，包括他们的姓名、年龄、地址和工资等。
CREATE TABLE CUSTOMERS (
ID INT NOT NULL,
NAME VARCHAR (20) NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR (25),
SALARY DECIMAL (18, 2),
PRIMARY KEY (ID)
);现在使用 INSERT 语句向该表中插入值，如下所示：
INSERT INTO CUSTOMERS VALUES
(1, 'Ramesh', 32, 'Ahmedabad', 2000.00 ),
(2, 'Khilan', 25, 'Delhi', 1500.00 ),
(3, 'Kaushik', 23, 'Kota', 2000.00 ),
(4, 'Chaitali', 25, 'Mumbai', 6500.00 ),
(5, 'Hardik', 27, 'Bhopal', 8500.00 ),
(6, 'Komal', 22, 'Hyderabad', 4500.00 ),
(7, 'Muffy', 24, 'Indore', 10000.00 );该表将被创建为：
让我们创建另一个名为 ORDERS 的表，其中包含所做的订单和下单日期的详细信息。
CREATE TABLE ORDERS (
OID INT NOT NULL,
DATE VARCHAR (20) NOT NULL,
CUSTOMER_ID INT NOT NULL,
AMOUNT DECIMAL (18, 2),
);使用 INSERT 语句像下面这样向该表中插入值：
INSERT INTO ORDERS VALUES
(102, '2009-10-08 00:00:00', 3, 3000.00),
(100, '2009-10-08 00:00:00', 3, 1500.00),
(101, '2009-11-20 00:00:00', 2, 1560.00),
(103, '2008-05-20 00:00:00', 4, 2060.00);该表显示如下：
Right join Query
Now, let us join these two tables using the Right Join query as follows.
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;Joining Multiple Tables with Right Join
与左侧连接类似，右侧连接也会连接多个表格。然而，区别在于右侧表格会整体返回，而不是左侧表格。
Syntax
以下是使用右侧连接来连接多个表格的语法：
SELECT column1, column2, column3...
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name
RIGHT JOIN table3
ON table2.column_name = table3.column_name
.
.
.Example
Here, let us consider the previously created tables CUSTOMERS and ORDERS; along with the newly created table EMPLOYEE.
We will create the EMPLOYEE table using the query below −
CREATE TABLE EMPLOYEE (
EID INT NOT NULL,
EMPLOYEE_NAME VARCHAR (30) NOT NULL,
SALES_MADE DECIMAL (20)
);现在，我们可以使用 INSERT 语句将值插入到此空表中，如下所示：
INSERT INTO EMPLOYEE VALUES
(102, 'SARIKA', 4500),
(100, 'ALEKHYA', 3623),
(101, 'REVATHI', 1291),
(103, 'VIVEK', 3426);表创建如下 −
Let us join these three tables using the Right Join query given below −
SELECT CUSTOMERS.ID, CUSTOMERS.NAME, ORDERS.DATE, EMPLOYEE.EMPLOYEE_NAME
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
RIGHT JOIN EMPLOYEE
ON ORDERS.OID = EMPLOYEE.EID;Through this query, we are trying to display the records of Customer IDs, Customer names, Orders made on specific dates and names of the employees that sold them.
Right Join with WHERE Clause
A WHERE Clause is used to filter out records that satisfy the condition specified by it. This clause can be used with the Right Join technique to apply constraints on the result-set obtained.
Syntax
使用 WHERE 子句时的右侧连接语法如下：
SELECT column_name(s)
FROM table_name1
RIGHT JOIN table_name2
ON table_name1.column_name = table_name2.column_name
WHERE conditionExample
Records in the combined database tables can be filtered using the WHERE clause. Consider the previous two tables CUSTOMERS and ORDERS; and join them using the following query −
SELECT ID, NAME, DATE, AMOUNT FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
WHERE ORDERS.AMOUNT > 1000.00;