PHP MySQLi 封装类完整版

<?php
/**
 * MysqliDb Class
 *
 * @category  Database Access
 * @package   MysqliDb
 * @author    Jeffery Way <[email protected]>
 * @author    Josh Campbell <[email protected]>
 * @author    Alexander V. Butenko <[email protected]>
 * @copyright Copyright (c) 2010-2016
 * @license   https://opensource.org/licenses/gpl-3.0.html GNU Public License
 * @link      https://github.com/joshcam/PHP-MySQLi-Database-Class 
 * @version   2.8-master
 */


class MysqliDb
{


    /**
     * Static instance of self
     * @var MysqliDb
     */
    protected static $_instance;


    /**
     * Table prefix
     * @var string
     */
    public static $prefix = '';


    /**
     * MySQLi instances
     * @var mysqli[]
     */
    protected $_mysqli = [];


    /**
     * The SQL query to be prepared and executed
     * @var string
     */
    protected $_query;


    /**
     * The previously executed SQL query
     * @var string
     */
    protected $_lastQuery;


    /**
     * The SQL query options required after SELECT, INSERT, UPDATE or DELETE
     * @var array
     */
    protected $_queryOptions = array();


    /**
     * An array that holds where joins
     * @var array
     */
    protected $_join = array();


    /**
     * An array that holds where conditions
     * @var array
     */
    protected $_where = array();


    /**
     * An array that holds where join ands
     *
     * @var array
     */
    protected $_joinAnd = array();


    /**
     * An array that holds having conditions
     * @var array
     */
    protected $_having = array();


    /**
     * Dynamic type list for order by condition value
     * @var array
     */
    protected $_orderBy = array();


    /**
     * Dynamic type list for group by condition value
     * @var array
     */
    protected $_groupBy = array();
<?php
/**
 * MysqliDb Class
 *
 * @category  Da