title: why does this SQL not work when both fields are included
body: <p>So this first SQL returns zero rows:</p>
  
  <pre><code>SELECT b.b_id 
  FROM `buy` b 
      INNER JOIN `buy_multiples` AS bm 
          ON b.b_id = bm.b_id 
          AND b.buy_status IN (2)  
  WHERE bm.`option_type` = 'area_id'  
  AND bm.selected_option_key IN (10)
  AND bm.`option_type` = 'bzips'  
  AND bm.selected_option_key IN (37027)
  GROUP BY b.b_id 
  </code></pre>
  
  <p>This second SQL returns b_id 5024 and 4987:</p>
  
  <pre><code>SELECT b.b_id 
  FROM `buy` b 
      INNER JOIN `buy_multiples` AS bm 
          ON b.b_id = bm.b_id 
          AND b.buy_status IN (2)  
  WHERE bm.`option_type` = 'bzips'  
  AND bm.selected_option_key IN (37027)
  GROUP BY b.b_id 
  </code></pre>
  
  <p>This third SQL returns b_id 5024 and 4987 and 4989:</p>
  
  <pre><code>SELECT b.b_id 
  FROM `buy` b 
      INNER JOIN `buy_multiples` AS bm 
          ON b.b_id = bm.b_id 
          AND b.buy_status IN (2)  
  WHERE bm.`option_type` = 'area_id'  
  AND bm.selected_option_key IN (10)
  GROUP BY b.b_id 
  </code></pre>
  
  <p>Why the first one returns zero rows?</p>