title: MYSQL Select column name from other select
body: <p>I want to select <code>colum1 + column2 + column3</code> from one table but the problem is that the columns' names came from a script I can't change. </p>
  
  <p>So I have</p>
  
  <pre><code>select column1,column2,column3 from table
  </code></pre>
  
  <p>but I need the sum of them. Can this be done? I tried:</p>
  
  <pre><code>select(select REPLACE(...))
  </code></pre>
  
  <p>it's not working.</p>
  
  <p>Other way - no success, was:</p>
  
  <pre><code>select sum() from 
  (
      select column1,column2,column3 from table
  )
  </code></pre>