Hello Guys,
We can create a custom resource model in Magento2 using following custom module extension and can use it for querying the database with our custom SQL statements and collections.

Let's create a resource model with following steps defined.

Step 1: We need to create an module.xml in app/code/Magemeta/Override/etc/module.xml to register our custom module.

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/Module/etc/module.xsd">
    <module name="Magemeta_Override" setup_version="1.0.0"/>
</config>

Step 2: We need to create an Test.php in app/code/Magemeta/Override/Model/ResourceModel/Test.php to register our custom resource model class. In this class, we have declared _construct() method where we will initialise our custom resource model with it's associated table with primary key which will act as a main table for this resource model.

<?php
namespace Magemeta\Override\Model\ResourceModel;

use Magento\Framework\Model\ResourceModel\Db\AbstractDb;
/**
* Class Test
* @package Magemeta\Override\Model\ResourceModel
*/
class Test extends AbstractDb
{
    /**
     * Test constructor.
     * @param \Magento\Framework\Model\ResourceModel\Db\Context $context
     */
    public function __construct(
        \Magento\Framework\Model\ResourceModel\Db\Context $context
    )
    {
        parent::__construct($context);
    }

    /**
     * Initialize ResourceModel
     */
    protected function _construct()
    {
        $this->_init('catalog_product_entity', 'entity_id'); // initialize table with it's primary key
    }

    /**
     * @return mixed
     */
    protected function getMainTable()
    {
        return $this->getMainTable(); // catalog_product_entity
    }
}

And this is our custom resource model we have created using small module extension. Cheers! Hope this helps you guys!