1.最简单的方式-mysql（面向过程）

<?php
$con = mysql_connect("localhost","root","password");
$select_db = mysql_select_db('test');
if (!$select_db) {die("could not connect to the db:\n" .  mysql_error());
}//查询代码
$sql = "select * from db_table";
$res = mysql_query($sql);
if (!$res) {die("could get the res:\n" . mysql_error());
}
while ($row = mysql_fetch_assoc($res)) {print_r($row);
}
//查询代码//关闭数据库连接
mysql_close($con);
?>

2.新的方式-mysqli（面向过程）

$mysql_server_name = 'localhost'; //改成自己的mysql数据库服务器
$mysql_username = 'root'; //改成自己的mysql数据库用户名
$mysql_password = 'password'; //改成自己的mysql数据库密码
$mysql_database = 'test'; //改成自己的mysql数据库名
$conn=mysqli_connect($mysql_server_name,$mysql_username,$mysql_password,$mysql_database); //连接数据库
//连接数据库错误提示
if (mysqli_connect_errno($conn)) { die("连接 MySQL 失败: " . mysqli_connect_error()); 
}
mysqli_query($conn,"set names utf8"); //数据库编码格式// mysqli_set_charset($conn,"utf8");//设置默认客户端字符集。
// mysqli_select_db($conn,$mysql_database); //更改连接的默认数据库//查询代码
$sql = “select * from db_table”;
$query = mysqli_query($conn,$sql);
while($row = mysqli_fetch_array($query)){echo $row['title'];
}
//查询代码// 释放结果集+关闭MySQL数据库连接
mysqli_free_result($result);
mysqli_close($conn); 

3、常用方式-mysqli（面向对象）

//连接数据库方式1
$conn = new mysqli('localhost', 'root', 'password', 'test');//连接数据库方式2
// $conn = new mysqli();
// $conn -> connect('localhost', 'root', 'password', 'test');//check connection (检查PHP是否连接上MYSQL)
if ($conn -> connect_errno) {printf("Connect failed: %s\n", $conn->connect_error);exit();
}//查询代码
$sql = “select * from db_table”;
$query = $conn->query($sql);
while($row = $query->fetch_array()){echo $row['title'];
}
//查询代码//释放结果集+关闭MySQL连接
$query1 -> free_result();
$conn -> close();

4、PDO连接MySQL数据库

<?php
$db = new PDO('mysql:host=localhost;dbname=test', 'root', 'password');
try {foreach ($db->query('select * from db_table') as $row){print_r($row);}$db = null; //关闭数据库
} catch (PDOException $e) {echo $e->getMessage();
}
?>

5、ADODB连接MySQL数据库

<?php
//安装驱动-引入类即可
require_once './adodb5/adodb.inc.php';
$conn = &ADONewConnection('mysql');
$conn->connect('localhost','root','password','test');
$conn->Execute("set names utf8");
//查询代码
$res = $conn->Execute("select * from db_table");
if (!$res){echo $conn->ErrorMsg();
}else{var_dump($res);
}
?>//关闭连接
$conn->close();

6、总结-关闭mysql数据库的连接方法

MySQL - 面向过程mysql_close($conn);MySQLi - 面向过程mysqli_close($conn);MySQLi - 面向对象$conn->close();PDO$conn = null;ADODB$conn->close();
或$conn->free();