mysql连接数据库怎么写

import mysql.connector

# 建立数据库连接
cnx = mysql.connector.connect(user='username', password='password', host='hostname', database='database_name')

# 创建游标对象
cursor = cnx.cursor()

# 执行SQL查询语句
query = "SELECT * FROM table_name"
cursor.execute(query)

# 获取查询结果
result = cursor.fetchall()

# 关闭游标和数据库连接
cursor.close()
cnx.close()

import java.sql.*;

// 建立数据库连接
Connection conn = DriverManager.getConnection("jdbc:mysql://hostname:port/database_name", "username", "password");

// 创建Statement对象
Statement stmt = conn.createStatement();

// 执行SQL查询语句
String query = "SELECT * FROM table_name";
ResultSet rs = stmt.executeQuery(query);

// 获取查询结果
while (rs.next()) {
    // 处理查询结果
}

// 关闭Statement对象和数据库连接
stmt.close();
conn.close();

<?php
// 建立数据库连接
$servername = "hostname";
$username = "username";
$password = "password";
$database = "database_name";

$conn = new mysqli($servername, $username, $password, $database);

// 检查连接是否成功
if ($conn->connect_error) {
    die("连接失败：" . $conn->connect_error);
}

// 执行SQL查询语句
$query = "SELECT * FROM table_name";
$result = $conn->query($query);

// 获取查询结果
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        // 处理查询结果
    }
}

// 关闭数据库连接
$conn->close();
?>