title: Multiply two columns and display in new one
body: <p>I am having 3 tables named <code>customers</code>,<code>cars</code>,<code>carrent</code>. All i want is to multiply <code>rentorder.days</code> with <code>cardetail.rentday</code> and show the value in <code>rentorder.totalrent</code>. I am unable to achieve this. How can i do this.
  Any suggestions please.</p>
  
  <p><strong>SQL</strong></p>
  
  <pre><code>SELECT customers.*, 
         cardetail.carname, 
         cardetail.model, 
         cardetail.company, 
         cardetail.color, 
         cardetail.rentday, 
         rentorder.days, 
         rentorder.totalrent 
  FROM   rentorder 
         INNER JOIN customers 
                 ON customers.custid = rentorder.custid 
         INNER JOIN cardetail 
                 ON cardetail.id = rentorder.carid 
  </code></pre>