title: Combined COUNTIF for several columns
body: <p>We have a table with values like this:</p>
  
  <p><img src="https://i.stack.imgur.com/eaB04.png" alt="enter image description here"></p>
  
  <p>I need a formula for cell <code>D1</code> to count rows that have in column <code>A</code> value "one" and column B is not empty. For example: </p>
  
  <ul>
  <li>in first row <code>A1==one</code> but <code>B1</code> is empty; (that doesn't count)</li>
  <li>in second row <code>A2==one</code> and <code>B2</code> is not empty; (that counts 1)</li>
  <li>...</li>
  <li>in 4th row <code>A4</code> is not equal to value "one" (that doesn't count)</li>
  </ul>
  
  <p>I know about formulas like <code>COUNTIF</code> and <code>COUNTIFS</code> but I can`t figure out how to use them with combined condition.</p>