title: MySQL query where column may be missing
body: <p>I have a Microsoft stored procedure that queries two MySQL databases using OpenQuery. The two MySQL databases should be have the same schemas, so I can run the same query on both.</p>
  
  <p>However, we will soon alter the MySQL schemas, and add a column to a table. But the two MySQL databases won't happen at the same time, and I don't know the exact date of the releases.</p>
  
  <p>I therefore want to write the query so that if the new column exists, then I use it in my select. If not, then I use a default value.</p>
  
  <p>Is this possible? (That is have a query that handles differences in the table schema?)</p>
  
  <p>(Not to be confused with 'coelesce' where the field definitely exists, but is simply null.)</p>