This tutorial will show you how we can use Codeigniter’s Query Builder Class to build join queries for fetching data from multiple tables.

The purpose of a join is to combine the data across tables.

A join is actually performed by the where clause which combines the specified rows of tables.

If a join involves in more than two tables then first two tables are joined based on the join condition and then compares the result with the next table and so on.

Here we will see Left Outer Join example. Outer join gives the non-matching records along with matching records. Left Outer Join will display the all matching records and the records which are in left hand side table those that are not in right hand side table.

We will use Codeigniter’s $this->db->join() that permits you to write the JOIN portion of your query.

Read also Codeigniter Full Outer Join Example ,  Codeigniter Right Outer Join Example and Codeigniter Join Example


Prerequisites

Netbeans 8.1
XAMPP in Windows
Codeigniter 3.0.6

Configure XAMPP and Netbeans

From Netbeans IDE go to Tools->Options. Click on PHP. Now on tab “General” browse the file for “PHP 5 Interpreter”. The php interpreter file generally placed inside the <physical drive in Windows OS>:xamppphpphp.exe

Configure Codeigniter and Netbeans

Create a new PHP project in Netbeans. Then remove the index.php file from the newly created project. Now copy the extracted files from Codeigniter 3.0.6 to the newly created project directory.

Directory Structure

A typical directory structure for the project would be as shown below.

codeigniter join

Example on Left Outer Join Query

Suppose we have blogs table with below data

sql join

And we have blog_comments table with below data

sql join

On executing below query

SELECT blogs.blog_id,comment_id,blog_title,blog_content,blog_date,comment_text,comment_date
 FROM blogs LEFT OUTER JOIN blog_comments ON blog_comments.blog_id = blogs.blog_id

We will get below results

left outer join

Step 1. Now modify <root directory>/application/config/autoload.php file for auto-loading html, url, file, form and session

$autoload['helper'] = array('html', 'url', 'file', 'form');

$autoload['libraries'] = array('database', 'session');

Step 2. Now modify <root directory>/application/config/config.php file to define encryption key

$config['encryption_key'] = '2d8+e6]K0?ocWp7&`K)>6Ky"|.x|%nuwafC~S/+6_mZI9/17y=sKKG.;Tt}k';

Step 3. Create a view file under <root directory>/application/views which will be used to display blogs

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Codeigniter Left Outer Join Example</title>
        <style type="text/css">
            ::selection { background-color: #E13300; color: white; }
            ::-moz-selection { background-color: #E13300; color: white; }

            body {
                background-color: #fff;
                margin: 40px;
                font: 13px/20px normal Helvetica, Arial, sans-serif;
                color: #4F5155;
            }            

            #body {
                margin: 0 15px 0 15px;
            }

            #container {
                margin: 10px;
                border: 1px solid #D0D0D0;
                box-shadow: 0 0 8px #D0D0D0;
            }

            h1 {
                margin-left: 15px;
            }

            .error {
                color: #E13300;
            }

            .success {
                color: darkgreen;
            }
        </style>
    </head>
    <body>
        <div id="container">
            <h1>CodeIgniter Left Outer Join Example</h1>            
            <div id="body">
                <?php
                foreach ($blogs as $blog) {
                    ?>
                    <div class="post">
                        <h2 class="title"><?php echo $blog->blog_title; ?></h2>
                        <p class="meta">
                            <?php
                            echo $blog->blog_date;
                            ?>
                        <div class="entry">
                            <p><?php echo $blog->blog_content; ?></p>
                        </div>
                    </div>
                <p>&nbsp;&nbsp;&nbsp;&nbsp;<strong>Comment on <?php echo $blog->comment_date; ?> :</strong> <?php echo $blog->comment_text; ?></p>
                    <?php
                }
                ?>
            </div>
        </div>
    </body>
</html>

Step 4. Create a Controller class under <root directory>/application/controllers for handling client’s request and response

<?php

defined('BASEPATH') OR exit('No direct script access allowed');

/**
 * Description of Blog
 *
 * @author https://www.roytuts.com
 */
class Blog extends CI_Controller {

    function __construct() {
        parent::__construct();
        $this->load->model('blogmodel');
    }

    public function index() {
        $data['blogs'] = $this->blogmodel->left_outer_join();
        $this->load->view('blog_left_outer_join', $data);
    }

}

Step 5. Create a Model class under <root directory>/application/models for performing database operatins

<?php

defined('BASEPATH') OR exit('No direct script access allowed');

/**
 * Description of BlogModel
 *
 * @author https://www.roytuts.com
 */
class BlogModel extends CI_Model {

    private $blogs = 'blogs';   // blog table
    private $blog_comments = 'blog_comments';   // blog comment table

    function __construct() {
        parent::__construct();
    }

    function left_outer_join() {
        $this->db->select($this->blogs . '.blog_id,comment_id,blog_title,blog_content,blog_date,comment_text,comment_date');
        $this->db->from($this->blogs);
        //third parameter indicates left outer join
        $this->db->join($this->blog_comments, $this->blog_comments . '.blog_id = ' . $this->blogs . '.blog_id', 'left outer');
        $query = $this->db->get();
        return $query->result();
    }

}

Step 6. Now modify <root directory>/application/config/routes.php file for pointing the default controller class

$route['default_controller'] = 'blog';

Step 7. Now if everything is fine run the application, you will see below output in the browser. For few blogs you will see comment date and for other blogs you will see no comment dates because in left outer join all records from left table and matching records from right table are fetched.
left outer join

Download MySQL script

blogs

Thanks for reading.

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