title: PostgreSQL multiplication of columns
body: <p>I have Postgres database and I have to multiply column by column like this:</p>
  
  <pre><code>SELECT SUM(column1*column2) AS res (...)
  </code></pre>
  
  <p>And the result is <code>0</code>. Both columns are <code>real</code> type.<br>
  But the multiplication operator works great when I do:</p>
  
  <pre><code>SELECT SUM(column * 100) AS res (...)
  </code></pre>
  
  <p>Is it possible to do arithmetics using columns in PostgreSQL?</p>