title: PostgreSQL select columns based on case statement
body: <p>I have the following sql query: </p>
  
  <pre><code>SELECT id, first_name, last_name FROM users;
  </code></pre>
  
  <p>Now I want to add a case statement with the following clauses:</p>
  
  <pre><code> 1. If 1+1 == 2 then show only id column
   2. If 1+2 == 2 then show only first_name column
   3. If 1+3 == 3 then show only last_name column
  </code></pre>
  
  <p>This is only stupid example but should describe what I'm looking for. Is there a way to do this in PostgreSQL?</p>