title: Union query with different numbers of columns
body: <p>It is for sure a simple question but I can't fix an MySQL query: 
  I want to run below prepared query</p>
  
  <pre><code>select id from table1 where c_id = :c_id 
  union 
  select id,name from table2 where c_id = :c_id and temp = :temp
  </code></pre>
  
  <p>So I have different numbers of column in each table select's output. Is this the reason it is not working?</p>