MySQL - Cross Join 交叉连接
MySQL Cross Join 交叉连接
MySQL 交叉连接 将第一个表的每一行与第二个表的每一行合并。它是一种基本的内连接类型,用于检索两个独立表(即排列)的笛卡尔积(或叉积)。
笛卡尔积(或叉积)是两个集合相乘的结果。这是通过将两个集合中所有可能的对相乘来实现的。
下图以简单的方式说明了交叉连接。
语法
以下是 MySQL 中交叉连接查询的基本语法 -
SELECT column_name(s) FROM table1 CROSS JOIN table2
示例
在此交叉连接示例中,我们首先创建一个名为 CUSTOMERS 的表,其中包含客户的个人信息,包括姓名、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 语句将值插入到该表中,如下所示 -
INSERT INTO CUSTOMERS VALUES (1, 'Ramesh', 32, 'Ahmedabad', 2000.00 ), (2, 'Khilan', 25, 'Delhi', 1500.00 );
该表将创建为 −
| ID | NAME | AGE | ADDRESS | SALARY |
|---|---|---|---|---|
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
让我们创建另一个表 ORDERS,其中包含已下订单的详细信息及其下单日期。
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,将值插入此表,如下所示 -
INSERT INTO ORDERS VALUES (100, '2009-10-08 00:00:00', 3, 1500.00), (101, '2009-11-20 00:00:00', 2, 1560.00);
表显示如下 −
| OID | DATE | CUSTOMER_ID | AMOUNT |
|---|---|---|---|
| 100 | 2009-10-08 00:00:00 | 3 | 1500.00 |
| 101 | 2009-11-20 00:00:00 | 2 | 1560.00 |
现在,如果我们对上面给出的两个表执行以下交叉连接查询,交叉连接会将 CUSTOMERS 表中的每一行与 ORDERS 表中的每一行合并。
SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS CROSS JOIN ORDERS;
输出
结果表如下 -
| ID | NAME | AMOUNT | DATE |
|---|---|---|---|
| 2 | Khilan | 1500.00 | 2009-10-08 00:00:00 |
| 1 | Ramesh | 1560 | 2009-11-20 00:00:00 |
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 |
| 1 | Ramesh | 1500.00 | 2009-10-08 00:00:00 |
使用交叉连接连接多个表
我们也可以使用交叉连接来连接两个以上的表。在这种情况下,会显示多向排列,并且预期结果表包含的记录数量将远多于单个表。
语法
以下是在 MySQL 中使用交叉连接连接多个表的语法 -
SELECT column_name(s) FROM table1 CROSS JOIN table2 CROSS JOIN table3 CROSS JOIN table4 . . .
示例
现在让我们合并三个表 CUSTOMERS、ORDERS 和 ORDER_RANGE,以演示如何使用交叉连接合并多个表。
我们将使用以下查询创建 ORDER_RANGE 表 -
CREATE TABLE ORDER_RANGE ( SNO INT NOT NULL, ORDER_RANGE VARCHAR (20) NOT NULL, );
现在,我们可以使用 INSERT 语句将值插入到这个空表中,如下所示 -
INSERT INTO ORDER_RANGE VALUES (1, '1-100'), (2, '100-200'), (3, '200-300');
ORDER_RANGE 表如下 −
| SNO | ORDER_RANGE |
|---|---|
| 1 | 1-100 |
| 2 | 100-200 |
| 3 | 200-300 |
现在我们对给定的表使用以下交叉连接查询,
SELECT ID, NAME, AMOUNT, DATE, ORDER_RANGE FROM CUSTOMERS CROSS JOIN ORDERS CROSS JOIN ORDER_RANGE;
输出
结果表如下 -
| ID | NAME | AMOUNT | DATE | ORDER_RANGE |
|---|---|---|---|---|
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 | 1-100 |
| 1 | Ramesh | 1560 | 2009-11-20 00:00:00 | 1-100 |
| 2 | Khilan | 1500.00 | 2009-10-08 00:00:00 | 1-100 |
| 1 | Ramesh | 1500.00 | 2009-10-08 00:00:00 | 1-100 |
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 | 100-200 |
| 1 | Ramesh | 1560 | 2009-11-20 00:00:00 | 100-200 |
| 2 | Khilan | 1500.00 | 2009-10-08 00:00:00 | 100-200 |
| 1 | Ramesh | 1500.00 | 2009-10-08 00:00:00 | 100-200 |
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 | 200-300 |
| 1 | Ramesh | 1560 | 2009-11-20 00:00:00 | 200-300 |
| 2 | Khilan | 1500.00 | 2009-10-08 00:00:00 | 200-300 |
| 1 | Ramesh | 1500.00 | 2009-10-08 00:00:00 | 200-300 |
使用客户端程序进行交叉连接
我们也可以使用客户端程序对一个或多个表执行交叉连接操作。
语法
要通过 PHP 程序执行交叉连接,我们需要使用 mysqli 函数 query() 执行带有 CROSS JOIN 子句的 SQL 查询,如下所示 -
$sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a CROSS JOIN tcount_tbl b"; $mysqli->query($sql);
要通过 JavaScript 程序执行交叉连接,我们需要使用 mysql2 库的 query() 函数执行带有 CROSS JOIN 子句的 SQL 查询,如下所示 -
sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a CROSS JOIN tcount_tbl b"; con.query(sql);
要通过 Java 程序执行交叉连接,我们需要使用 JDBC 函数 executeQuery() 执行带有 CROSS JOIN 子句的 SQL 查询,如下所示 -
String sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a CROSS JOIN tcount_tbl b ON a.tutorial_author = b.tutorial_author"; statement.executeQuery(sql);
要通过 Python 程序执行交叉连接,我们需要使用 MySQL Connector/Python 的 execute() 函数执行带有 CROSS JOIN 子句的 SQL 查询,如下所示 -
cross_join_query = "SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS CROSS JOIN ORDERS" cursorObj.execute(cross_join_query)
示例
以下是程序 -
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'password';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if ($mysqli->connect_errno) {
printf("Connect failed: %s
", $mysqli->connect_error);
exit();
}
// printf('Connected successfully.
');
$sql = 'SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count
FROM tutorials_tbl a CROSS JOIN tcount_tbl b';
$result = $mysqli->query($sql);
if ($result->num_rows > 0) {
echo " following is the details after executing cross join!
";
while ($row = $result->fetch_assoc()) {
printf("Id: %s, Author: %s, Count: %d", $row["tutorial_id"], $row["tutorial_author"], $row["tutorial_count"]);
printf("
");
}
} else {
printf('No record found.
');
}
mysqli_free_result($result);
$mysqli->close();
输出
获得的输出如下 -
following is the details after executing cross join! Id: 102, Author: Sarika Singh, Count: 20 Id: 101, Author: Aman kumar, Count: 20 Id: 3, Author: Sanjay, Count: 20 Id: 2, Author: Abdul S, Count: 20 Id: 1, Author: John Poul, Count: 20 Id: 102, Author: Sarika Singh, Count: 5 Id: 101, Author: Aman kumar, Count: 5 Id: 3, Author: Sanjay, Count: 5 Id: 2, Author: Abdul S, Count: 5 Id: 1, Author: John Poul, Count: 5 Id: 102, Author: Sarika Singh, Count: 4 Id: 101, Author: Aman kumar, Count: 4 Id: 3, Author: Sanjay, Count: 4 Id: 2, Author: Abdul S, Count: 4 Id: 1, Author: John Poul, Count: 4 Id: 102, Author: Sarika Singh, Count: 20 Id: 101, Author: Aman kumar, Count: 20 Id: 3, Author: Sanjay, Count: 20 Id: 2, Author: Abdul S, Count: 20 Id: 1, Author: John Poul, Count: 20 Id: 102, Author: Sarika Singh, Count: 1 Id: 101, Author: Aman kumar, Count: 1 Id: 3, Author: Sanjay, Count: 1 Id: 2, Author: Abdul S, Count: 1 Id: 1, Author: John Poul, Count: 1 Id: 102, Author: Sarika Singh, Count: 1 Id: 101, Author: Aman kumar, Count: 1 Id: 3, Author: Sanjay, Count: 1 Id: 2, Author: Abdul S, Count: 1 Id: 1, Author: John Poul, Count: 1
var mysql = require("mysql2");
var con = mysql.createConnection({
host: "localhost",
user: "root",
password: "password",
}); //连接到 MySQL
con.connect(function (err) {
if (err) throw err;
// console.log("Connected successfully...!");
// console.log("--------------------------");
sql = "USE TUTORIALS";
con.query(sql);
//Cross Join
sql =
"SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a CROSS JOIN tcount_tbl b";
con.query(sql, function (err, result) {
if (err) throw err;
console.log(result);
});
});
输出
生成的输出如下 -
[
{
tutorial_id: 102,
tutorial_author: 'Sarika Singh',
tutorial_count: 20
},
{
tutorial_id: 101,
tutorial_author: 'Aman kumar',
tutorial_count: 20
},
{ tutorial_id: 2, tutorial_author: 'Abdul S', tutorial_count: 20 },
{ tutorial_id: 1, tutorial_author: 'John Poul', tutorial_count: 20 },
{
tutorial_id: 102,
tutorial_author: 'Sarika Singh',
tutorial_count: 5
},
{
tutorial_id: 101,
tutorial_author: 'Aman kumar',
tutorial_count: 5
},
{ tutorial_id: 2, tutorial_author: 'Abdul S', tutorial_count: 5 },
{ tutorial_id: 1, tutorial_author: 'John Poul', tutorial_count: 5 },
{
tutorial_id: 102,
tutorial_author: 'Sarika Singh',
tutorial_count: 4
},
{
tutorial_id: 101,
tutorial_author: 'Aman kumar',
tutorial_count: 4
},
{ tutorial_id: 2, tutorial_author: 'Abdul S', tutorial_count: 4 },
{ tutorial_id: 1, tutorial_author: 'John Poul', tutorial_count: 4 },
{
tutorial_id: 102,
tutorial_author: 'Sarika Singh',
tutorial_count: 20
},
{
tutorial_id: 101,
tutorial_author: 'Aman kumar',
tutorial_count: 20
},
{ tutorial_id: 2, tutorial_author: 'Abdul S', tutorial_count: 20 },
{ tutorial_id: 1, tutorial_author: 'John Poul', tutorial_count: 20 },
{
tutorial_id: 102,
tutorial_author: 'Sarika Singh',
tutorial_count: 1
},
{
tutorial_id: 101,
tutorial_author: 'Aman kumar',
tutorial_count: 1
},
{ tutorial_id: 2, tutorial_author: 'Abdul S', tutorial_count: 1 },
{ tutorial_id: 1, tutorial_author: 'John Poul', tutorial_count: 1 },
{
tutorial_id: 102,
tutorial_author: 'Sarika Singh',
tutorial_count: 1
},
{
tutorial_id: 101,
tutorial_author: 'Aman kumar',
tutorial_count: 1
},
{ tutorial_id: 2, tutorial_author: 'Abdul S', tutorial_count: 1 },
{ tutorial_id: 1, tutorial_author: 'John Poul', tutorial_count: 1 },
{
tutorial_id: 102,
tutorial_author: 'Sarika Singh',
tutorial_count: 2
},
{
tutorial_id: 101,
tutorial_author: 'Aman kumar',
tutorial_count: 2
},
{ tutorial_id: 2, tutorial_author: 'Abdul S', tutorial_count: 2 },
{ tutorial_id: 1, tutorial_author: 'John Poul', tutorial_count: 2 }
]
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class CrossJoin {
public static void main(String[] args) {
String url = "jdbc:mysql://localhost:3306/TUTORIALS";
String username = "root";
String password = "password";
try {
Class.forName("com.mysql.cj.jdbc.Driver");
Connection connection = DriverManager.getConnection(url, username, password);
Statement statement = connection.createStatement();
System.out.println("Connected successfully...!");
//MySQL CROSS JOIN...!;
String sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a CROSS JOIN tcount_tbl b ON a.tutorial_author = b.tutorial_author";
ResultSet resultSet = statement.executeQuery(sql);
System.out.println("Table records after CROSS Join...!");
while (resultSet.next()){
System.out.println(resultSet.getString(1)+ " "+ resultSet.getString(2)+" "+resultSet.getString(3));
}
connection.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
输出
获得的输出如下所示 -
Connected successfully...! Table records after CROSS Join...! 1 John Paul 1 3 Sanjay 1
import mysql.connector
#建立连接
connection = mysql.connector.connect(
host='localhost',
user='root',
password='password',
database='tut'
)
cursorObj = connection.cursor()
cross_join_query = f"""SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS CROSS JOIN ORDERS"""
cursorObj.execute(cross_join_query)
# 获取所有符合条件的行
filtered_rows = cursorObj.fetchall()
for row in filtered_rows:
print(row)
cursorObj.close()
connection.close()
输出
以下是上述代码的输出 -
(1, 'Ramesh', 2060, '2008-05-20 00:00:00') (1, 'Ramesh', 1560, '2009-11-20 00:00:00') (1, 'Ramesh', 1500, '2009-10-08 00:00:00') (1, 'Ramesh', 3000, '2009-10-08 00:00:00') (2, 'Khilan', 2060, '2008-05-20 00:00:00') (2, 'Khilan', 1560, '2009-11-20 00:00:00') (2, 'Khilan', 1500, '2009-10-08 00:00:00') (2, 'Khilan', 3000, '2009-10-08 00:00:00') (3, 'kaushik', 2060, '2008-05-20 00:00:00') (3, 'kaushik', 1560, '2009-11-20 00:00:00') (3, 'kaushik', 1500, '2009-10-08 00:00:00') (3, 'kaushik', 3000, '2009-10-08 00:00:00') (4, 'Chaital', 2060, '2008-05-20 00:00:00') (4, 'Chaital', 1560, '2009-11-20 00:00:00') (4, 'Chaital', 1500, '2009-10-08 00:00:00') (4, 'Chaital', 3000, '2009-10-08 00:00:00') (5, 'Hardik', 2060, '2008-05-20 00:00:00') (5, 'Hardik', 1560, '2009-11-20 00:00:00') (5, 'Hardik', 1500, '2009-10-08 00:00:00') (5, 'Hardik', 3000, '2009-10-08 00:00:00') (6, 'Komal', 2060, '2008-05-20 00:00:00') (6, 'Komal', 1560, '2009-11-20 00:00:00') (6, 'Komal', 1500, '2009-10-08 00:00:00') (6, 'Komal', 3000, '2009-10-08 00:00:00') (7, 'Muffy', 2060, '2008-05-20 00:00:00') (7, 'Muffy', 1560, '2009-11-20 00:00:00') (7, 'Muffy', 1500, '2009-10-08 00:00:00') (7, 'Muffy', 3000, '2009-10-08 00:00:00')

