Product search: include SKU matching

add_filter( 'posts_join', function( $join, $query ) {

	if(
		! $query->is_main_query()
		|| is_admin()
		|| ! is_search()
		|| ! is_woocommerce()
	) {
		return $join;
	}

	global $wpdb;

	$join .= " LEFT JOIN {$wpdb->postmeta} ccom_post_meta"
		 . " ON {$wpdb->posts}.ID = ccom_post_meta.post_id ";

	return $join;
}, 10, 2 );

add_filter( 'posts_where', function( $where, $query ) {

	if(
		! $query->is_main_query()
		|| is_admin()
		|| ! is_search()
		|| ! is_woocommerce()
	) {
		return $where;
	}

	global $wpdb;

	$where = preg_replace(
		"/\(\s*{$wpdb->posts}.post_title\s+LIKE\s*(\'[^\']+\')\s*\)/",
		"( {$wpdb->posts}.post_title LIKE $1 )"
			. " OR ( ccom_post_meta.meta_key = '_sku'"
			. " AND ccom_post_meta.meta_value LIKE $1 )",
		$where
	);

	return $where;

}, 10, 2 );