MySQL - Inner Join 内连接

要通过 JavaScript 程序使用 Inner Join 操作连接具有公共字段的表，我们需要使用 mysql2 库的 query() 函数执行 JOIN 子句，如下所示 -

sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a
INNER JOIN tcount_tbl b ON a.tutorial_author = b.tutorial_author";
con.query(sql);

要通过 Java 程序使用 Inner Join 操作连接具有公共字段的表，我们需要使用 JDBC 函数 executeQuery() 执行 JOIN 子句，如下所示 -

String sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a
INNER JOIN tcount_tbl b ON a.tutorial_author = b.tutorial_author";
st.executeQuery(sql);

要通过 Python 程序使用 Inner Join 操作连接具有公共字段的表，我们需要使用 MySQL Connector/Python 的 execute() 函数执行 JOIN 子句，如下所示 -

using_inner_join_query = "SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS INNER JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUST_ID"
cursorObj.execute(using_inner_join_query)

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);
  //inner join
  sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count  FROM tutorials_tbl a INNER JOIN tcount_tbl b  ON a.tutorial_author = b.tutorial_author";
  con.query(sql, function (err, result) {
    if (err) throw err;
    console.log(result);
  });
});        

输出

生成的输出如下 -

[ { 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 InnerJoin {
   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 INNER JOIN...!;
         String sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a INNER JOIN tcount_tbl b ON a.tutorial_author = b.tutorial_author";
         ResultSet resultSet = statement.executeQuery(sql);
         System.out.println("Table records after INNER 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 -

Table records after INNER 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()
inner_join_query = f"""SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS INNER JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUST_ID """
cursorObj.execute(inner_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 -

(3, 'kaushik', 3000, '2009-10-08 00:00:00')
(3, 'kaushik', 1500, '2009-10-08 00:00:00')
(2, 'Khilan', 1560, '2009-11-20 00:00:00')
(4, 'Chaital', 2060, '2008-05-20 00:00:00')