示例1：
<?php
$data = array(
   array(
      'title' => 'My title' ,
      'name' => 'My Name' ,
      'date' => 'My date'
   ),
   array(
      'title' => 'Another title' ,
      'name' => 'Another Name' ,
      'date' => 'Another date'
   )
);

$this->db->insert_batch('mytable', $data); 

//生成： INSERT INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date'), ('Another title', 'Another name', 'Another date')