title: Variable within double quotes
body: <p>Which is the correct syntax?</p>
  
  <pre><code>$current_renewal_date = $wpdb-&gt;get_results(
                      "
                      SELECT expiry_date
                      FROM bid_tag
                      WHERE id = $renewal_tag_id
                      LIMIT 1
                      "
                  );
  </code></pre>
  
  <p>OR</p>
  
  <pre><code>$current_renewal_date = $wpdb-&gt;get_results(
                      "
                      SELECT expiry_date
                      FROM bid_tag
                      WHERE id = {$renewal_tag_id}
                      LIMIT 1
                      "
                  );
  </code></pre>