php7 兼容 MySQL 相关函数

如果之前的项目是用php5.6或者更早版本开发的，现在升级到php7+，那么很多和sql相关的操作代码就要改了，为了同时兼容php的新老版本，就用如下函数即可，参考了discuz的写法

if(!function_exists('mysql_pconnect')){
    $mysqli = mysqli_connect("$dbhost:$dbport", $dbuser, $dbpass, $dbname);
    function mysql_pconnect($dbhost, $dbuser, $dbpass){
        global $dbport;
        global $dbname;
        global $mysqli;
        $mysqli = mysqli_connect("$dbhost:$dbport", $dbuser, $dbpass, $dbname);
        return $mysqli;
        }
    function mysql_select_db($dbname){
        global $mysqli;
        return mysqli_select_db($mysqli,$dbname);
        }
    function mysql_fetch_array($result){
        return mysqli_fetch_array($result);
        }
    function mysql_fetch_assoc($result){
        return mysqli_fetch_assoc($result);
        }
    function mysql_fetch_row($result){
        return mysqli_fetch_row($result);
        }
    function mysql_query($query){
        global $mysqli;
        return mysqli_query($mysqli,$query);
        }
    function mysql_escape_string($data){
        global $mysqli;
        return mysqli_real_escape_string($mysqli, $data);
        //return addslashes(trim($data));
        }
    function mysql_real_escape_string($data){
        return mysql_real_escape_string($data);
        }
    function mysql_close(){
        global $mysqli;
        return mysqli_close($mysqli);
        }
}