How to create a separate layout for secondary pages in Joomla 3?

Question

Joomla

The task is to create a separate layout for displaying content. The idea is that the main page does not have a sidebar, but the secondary ones should have one.
For example, I want the layout on the main page to be like this:

<div class="header">
  HEADER
</div>
<div class="row">
  <div class="col-md-12">
    CONTENT
  </div>
</div>

But on the secondary pages it was like this:

<div class="header">
  HEADER
</div>
<div class="row">
  <div class="col-md-3">
    SIDEBAR
  </div>
  <div class="col-md-9">
    CONTENT
  </div>
</div>

Creating another template and installing it on the CMS as a separate template is a clumsy method that will only load the site system once again, but a more delicate solution would be found. Maybe it's in the redefinitions? I looked through it, but I did not find anything similar to the layout. On some templates (not mine), I saw that when creating a menu item, it was also possible to choose among several layouts of the same style. Thank you in advance!

Answer 1

In general, I found the answer for myself: if it is necessary to separate the layout of the main page (for example, the main page we have is a long landing page, and the secondary ones come with a sidebar), then you need to write a small php-construct in the index.php file located at the root of the folder template to define the main page.

<?php $myVar = $_SERVER['REQUEST_URI'];
if ($myVar == '/' or $myVar=='/index.php') {?>
<div>Its mainpage</div>
<?php } else {?>
<div>its secondpage</div>
<?php } ?>

Just instead of div blocks, you can include or request files with markup of the desired layout.
If there are any even simpler methods, then please, I will wait for answers!

Answer 2

What is wrong with the usual output of modules?
just then you choose that everywhere except the main one and that's it

<?php 
if ($this->countModules('position-1')) : ?>
<jdoc:include type="modules" name="position-1" style="none" />
<?php endif; ?>