How to fetch all the woocommerce products from the database using php

In order to fetch Single product to your single.php page you can make use of the code which i have already suggested over here. Refer here:

https://wordpress.stackexchange.com/questions/240653/how-to-query-single-product-in-woocommerce/240726#240726

In order to fetch All products that you have into your DB you can follow the steps below.

You can fetch the Woo-commerce Products based on the WP_Query also so that it is also saved in the wp_posts table alone. So that we might slightly modify the post type alone for getting the WP_Query to work on.

Step One: First We shall see to the parameters what we have to pass for the WP_Query.

$params = array(
        'posts_per_page' => 5, 
        'post_type' => 'product'
);

Note: As you can see, all we’ve done is added a post_type variable to the array, and set it’s value to "product"; the query will now look for WooCommerce products instead of posts.

Step Two: After that we have to run on with the same structure that the Normal WP_Query behaves.

<?php
$params = array(
        'posts_per_page' => 5, 
        'post_type' => 'product'
);
$wc_query = new WP_Query($params); 
?>
<?php if ($wc_query->have_posts()) :  ?>
<?php while ($wc_query->have_posts()) : $wc_query->the_post();  ?>
<?php the_title(); //Prints the title over Here ?>
<?php //You can add what ever you need from the loop over here ?>
<?php endwhile; ?>
<?php wp_reset_postdata(); ?>
<?php else:  ?>
<p>
     <?php _e( 'No Products' );  ?>
</p>
<?php endif; ?>

Explanations

• An array of parameters for WP_Query to work with is created; to start with it’s just the basic posts, but by adding more specifics to these parameters we can achieve different results for our queries.
• WP_Query is used to query the parameters created in the first line.
• The query is checked to see if it returned any results.
• If there are results, then we iterate over them:
  • First, setting the global variable $post, which ensures that the next function works.
  • Second, setting the the_title() variable, which is responsible for displaying the product title.
• Then, when the posts are displayed, we return the $post variable to its original state with thewp_reset_postdata function.

Using this link i have studied how to query the WooCommerce Products using WP_Query and I have shared here so that all might get used with this posts.

Happy Coding :)

Your code is working fine on my machine, However its seems some conflict to your previous wp query. You can also try to get all product like this..

<select Name='choose'>
<?php
$args = array( 'post_type' => 'product' ,'posts_per_page' => 100);
$products = get_posts( $args );
foreach( $products as $product ) : 
  echo '<option selected value="'.$product->post_title.'</option>';
endforeach;
?>
</select>

$this->db->select('*');
        $this->db->from('vm_posts');
        $this->db->join('vm_postmeta', 'vm_postmeta.post_id = vm_posts.id');
        $this->db->join('vm_wc_product_meta_lookup', 'vm_wc_product_meta_lookup.product_id = vm_postmeta.post_id');
        $this->db->join('vm_inventory', 'vm_wc_product_meta_lookup.sku = vm_inventory.product_sku');
        $this->db->join('vm_terms', 'vm_inventory.customer_id = vm_terms.name');
        $this->db->where('post_type','product');
        $query = $this->db->get()->result();