title: mysql min ignores null - need workaround/tweak
body: <p>For this query </p>
  
  <pre><code>SELECT min(date) min_date FROM  order_products group by order_id
  </code></pre>
  
  <p><code>min_date</code> ignores the <code>NULL</code> values in a group of order id.</p>
  
  <p>In my case I want min_date = NULL if the group has a order_products tuple with null value in date.</p>
  
  <p>Any idea how can I achieve this ?</p>