/**
 * [copyDb description] 备份数据库
 * @param [type] $dbname [description] 数据库名
 * @param [type] $fileName [description] 存储的文件名
 * @return [type]   [description]
 */
public function copyDb($dbname, $fileName){
	$myfile = fopen($fileName, "w") or die("Unable to open file!");//打开存储文件
	$this->link->query("use {$dbname}");//切换数据库
	$this->changeDb($dbname);
	$tables = $this->link->query('show tables');//获取当期数据库所有表名称
	while($re = $tables->fetch(PDO::FETCH_ASSOC)){
		//var_dump($re);//查看数组构成
		$tableName = $re['Tables_in_'.$dbname];//构成特定的下标
		$sql = "show create table {$tableName};";
		$tableSql = $this->link->query($sql);

		fwrite($myfile, "DROP TABLE IF EXISTS `{$tableName}`;\r\n");//加入默认删除表的遇见
		//下面备份表结构，这个循环之执行一次
		while($re = $tableSql->fetch(PDO::FETCH_ASSOC)){
			// echo "<pre>";
			// var_dump($re);
			// echo "</pre>";
			echo "正在备份表{$re['Table']}结构<br/>";
			fwrite($myfile, $re['Create Table'].";\r\n\r\n");
			echo "正在备份表{$re['Table']}结构完成<br/>";
		}
		//下面备份表数据
		echo "正在备份表{$tableName}数据<br/>";
		$sql = "select * from {$tableName};";
		$valueSql = $this->link->query($sql);
		while($re = $valueSql->fetch(PDO::FETCH_ASSOC)){
			$keyArr = array_keys($re);//获得对应的键值
			$valueArr = array_values($re);//获得对应的值
	
			$keyStr = '';
			foreach ($keyArr as $key => $value) {
				$keyStr .= "`".$value."`,";
			}
			$keyStr = substr($keyStr,0,strlen($keyStr)-1); //取出最后一个逗号


			$valueStr = '';
			// var_dump($valueArr);
			foreach ($valueArr as $key => $value) {
				$valueStr .= "'".$value."',";
			}
			//以上的处理只是对应sql的写法

			$valueStr = substr($valueStr,0,strlen($valueStr)-1); //取出最后一个逗号
			$sql = "insert into `{$tableName}`({$keyStr}) values({$valueStr})";
			fwrite($myfile, $sql.";\r\n\r\n");
			
		}
		echo "正在备份表{$tableName}数据完成<br/>";
		echo "<br/><hr/>";
	}
	fclose($myfile);
}