Ship code to the network, not to a server.

export default {
  async fetch(request, env) {
    const stmt = env.DB.prepare(
      'SELECT * FROM comments LIMIT 3');
    const { results } = await stmt.all();

    return new Response(renderHtml(results), {
      headers: { 'content-type': 'text/html' },
    });
  },
} satisfies ExportedHandler<Env>;

Query D1 from a Worker. The database arrives as a binding on env; no connection string in code. Adapted from the product page.