\begin{frame}
  \frametitle{Sorting Output}
  

  In some application scenarios it is necessary to \emph{add columns} 
  to a table to obtain suitable \emph{sorting criteria}.
  
  \begin{exampleblock}{}
    If the Students names were stored in the form \sql{\textquotesingle{}George\textvisiblespace{}Orwell\textquotesingle{}}, 
    sorting by last name is more or  less impossible.
    Having separate columns for first and last name is better. 
  \end{exampleblock}
  \pause\bigskip
  
  \emph{Null values} are all listed first or all listed last in
  the sorted sequence (depending on the database).
  \pause\bigskip
  
  \begin{goal}{}
    Since the effect of \sql{order by} is purely ``cosmetic'',\\
    \sql{order by} may \emph{not} be applied to a subquery.
  \end{goal}        
\end{frame}