如果在数据库中找不到，则用于搜索的Codeigniter代码语法

I just want to ask the syntax for the search box if the item you search is not in the database, here is my sample view.

<div id="content">

<script src="<?php echo base_url('assets/javascript/jquery.min.js') ?>"></script>

<h3>Edit Laptop and Desktop Information</h3>

<form action="editinventory" method="POST" id="frm_editslaptopdesktop" name="frm_editslaptopdesktop">
    Search User: <input type="text" id="txt_search" name="txt_search" size="30px"/>&nbsp;
    <input type="submit" id="btn_search" name="btn_search" value="Search"/>
</form>

I don't know what the code and where to put it so please can you help me? Thank you in advance. :)