mysql连接数据库语句怎么写

import mysql.connector

# 创建连接
mydb = mysql.connector.connect(
  host="localhost",
  user="username",
  password="password",
  database="database_name"
)

# 创建游标
mycursor = mydb.cursor()

# 执行查询
mycursor.execute("SELECT * FROM table_name")

# 获取结果
result = mycursor.fetchall()

# 输出结果
for row in result:
  print(row)

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class Main {
  public static void main(String[] args) {
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs = null;
    
    try {
      // 注册驱动
      Class.forName("com.mysql.jdbc.Driver");
      
      // 创建连接
      conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/database_name", "username", "password");
      
      // 创建Statement对象
      stmt = conn.createStatement();
      
      // 执行查询
      rs = stmt.executeQuery("SELECT * FROM table_name");
      
      // 处理结果
      while (rs.next()) {
        System.out.println(rs.getString(1) + " " + rs.getString(2));
      }
    } catch (SQLException e) {
      e.printStackTrace();
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    } finally {
      try {
        // 关闭连接
        if (rs != null) rs.close();
        if (stmt != null) stmt.close();
        if (conn != null) conn.close();
      } catch (SQLException e) {
        e.printStackTrace();
      }
    }
  }
}

<?php
// 创建连接
$conn = mysqli_connect("localhost", "username", "password", "database_name");

// 检查连接是否成功
if (mysqli_connect_errno()) {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  exit();
}

// 执行查询
$result = mysqli_query($conn, "SELECT * FROM table_name");

// 处理结果
while ($row = mysqli_fetch_assoc($result)) {
  echo $row["column_name1"] . " " . $row["column_name2"];
}

// 关闭连接
mysqli_close($conn);
?>