PHP连接和操作mysql数据库的工具类（单例模式）

直接上代码MySqlDBSingle.class.php

host = isset($config['host']) ? $config['host'] : '';
        $this->port = isset($config['port']) ? $config['port'] : '';
        $this->user = isset($config['user']) ? $config['user'] : '';
        $this->pwd = isset($config['pwd']) ? $config['pwd'] : '';
        $this->charset = isset($config['charset']) ? $config['charset'] : 'utf8';
        $this->dbname = isset($config['dbname']) ? $config['dbname'] : '';

    }

    /**
     * 连接数据库
     */
    private function connect()
    {
        $this->link = @mysql_connect("{$this->host}:{$this->port}", $this->user, $this->pwd) or die('数据库连接失败');
    }

    /**
     * 此方法用来执行sql语句
     * 如果是数据查询语句 成功返回结果集 失败返回false
     * 如果是数据操作语句 成功返回true   失败返回false
     * @param $sql
     * @return resource
     */
    public function query($sql)
    {
        if (!$result = mysql_query($sql, $this->link)) {
            echo 'sql语句执行失败
';
            echo '错误编号：' . mysql_errno(), '
';
            echo '错误信息：' . mysql_error(), '
';
            echo '错误的sql语句：' . $sql, '
';
            exit;
        }
        return $result;
    }

    /**
     * 设置字符集编码
     */
    private function setCharset()
    {
        $sql = "set names {$this->charset}";
        $this->query($sql);
    }

    /**
     * 选择数据库
     */
    private function selectDB()
    {
        $sql = "use {$this->dbname}";
        $this->query($sql);
    }

    /**
     * 私有的构造方法防止类的外部实例化对象
     * MySqlDBSingle constructor.
     * @param $config   连接数据库的参数
     */
    private function __construct($config)
    {
        $this->initParams($config);
        $this->connect();
        $this->setCharset();
        $this->selectDB();
    }

    /**
     * 私有的克隆方法 用来阻止类的外部克隆对象
     */
    private function __clone()
    {
        // TODO: Implement __clone() method.
    }

    /**
     * 公有的静态方法获取唯一的实例
     * @param array $config
     * @return MySqlDBSingle
     */
    public static function getInstance($config = array())
    {
        if (!self::$instance instanceof MySqlDBSingle) {
            self::$instance = new MySqlDBSingle($config);
        }
        return self::$instance;
    }

    /**
     * 从数据库获取所有数据
     * @param $sql
     * @param string $fetch_type    assoc|row|array
     * @return array                将表中的数据匹配成二维数组返回
     */
    public function fetchAll($sql, $fetch_type = 'assoc')
    {
        $rs = $this->query($sql);
        $fetch_types = array('assoc','row','array');
        if (!in_array($fetch_type,$fetch_types)) {
            $fetch_type = 'assoc';
        }
        $fetch_fun = 'mysql_f etch_'.$fetch_type;
        $array = array();
        while ($rows = $fetch_fun($rs)) {
            $array[] = $rows;
        }
        return $array;
    }

    /**
     * 查询列表的第一条记录
     * @param $sql
     * @param string $fetch_type
     * @return mixed|null
     */
    public function fetchRow($sql, $fetch_type = 'assoc') {
        $rs = $this->fetchAll($sql, $fetch_type);
        if(!empty($rs)) {
            return $rs[0];
        }
        return null;
    }

    /**
     * 查询列表的第一行第一列
     * @param $sql
     * @return null
     */
    public function fetchColumn($sql) {
        $rs = $this->fetchRow($sql,'row');
        if(!empty($rs)) {
            return $rs[0];
        }
        return null;
    }

}

$config = array(
    'host' => 'localhost',
    'port' => '3306',
    'user' => 'root',
    'pwd' => 'root',
    'charset' => 'utf8',
    'dbname' => 'mydatabase'
);
$db = MySqlDBSingle::getInstance($config);

$rs = $db->fetchAll("select * from my_student",'assoc');
echo '
';
var_dump($rs);echo '
';

$rs = $db->fetchRow("select * from my_student");
echo '
';
var_dump($rs);echo '
';

$rs = $db->fetchColumn("select * from my_student");
echo '
';
var_dump($rs);echo '
';