/**
 * [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);
}