WC search by sku

add_filter( 'the_posts', '__search_by_sku' );

function __search_by_sku( $posts ) {

	if ( is_admin() || ! is_search() ) {
		return $posts;
	}

	$ignoreIds = array( 0 );
	foreach ( $posts as $post ) {
		$ignoreIds[] = $post->ID;
	}

	$matchedSku = __get_parent_post_by_sku( get_search_query(), $ignoreIds );

	if ( $matchedSku ) {
		foreach ( $matchedSku as $product_id ) {
			$posts[] = get_post( $product_id->post_id );

		}

	}

	return $posts;
}

function __get_parent_post_by_sku( $sku, $ignoreIds ) {
	global $wpdb, $wp_query;

	$ignoreIdsForMySql = implode(",", $ignoreIds);
	$variationsSql = "
          SELECT p.post_parent as post_id FROM $wpdb->posts as p
          join $wpdb->postmeta pm
          on p.ID = pm.post_id
          and pm.meta_key='_sku'
          and pm.meta_value LIKE '%$sku%'
          join $wpdb->postmeta visibility
          on p.post_parent = visibility.post_id    
          and visibility.meta_key = '_visibility'
          and visibility.meta_value <> 'hidden'
            ";

	$variationsSql .= "
          where 1
          AND p.post_parent <> 0
          and p.ID not in ($ignoreIdsForMySql)
          and p.post_status = 'publish'
          group by p.post_parent
          ";

	$variations = $wpdb->get_results($variationsSql);

	foreach ( $variations as $post ) {
		$ignoreIds[] = $post->post_id;
	}

	$ignoreIdsForMySql = implode(",", $ignoreIds);

	$regularProductsSql =
		"SELECT p.ID as post_id FROM $wpdb->posts as p
        join $wpdb->postmeta pm
        on p.ID = pm.post_id
        and  pm.meta_key='_sku' 
        AND pm.meta_value LIKE '%$sku%' 
        join $wpdb->postmeta visibility
        on p.ID = visibility.post_id    
        and visibility.meta_key = '_visibility'
        and visibility.meta_value <> 'hidden'";

	$regularProductsSql .=
		"where 1
        and (p.post_parent = 0 or p.post_parent is null)
        and p.ID not in ($ignoreIdsForMySql)
        and p.post_status = 'publish'
        group by p.ID";

	$regular_products = $wpdb->get_results($regularProductsSql);

	$results = array_merge($variations, $regular_products);
	$wp_query->found_posts += sizeof($results);

	return $results;
}