\begin{frame}
  \frametitle{The From Clause}

%   \structureExercises
  
  \begin{goal}{}
  For each table in the \sql{from} clause there is a tuple variable.
  \end{goal}

  \begin{itemize}
  \pause
  
  \item If the the name of the tuple variable is not given explicitly, the variable will
    have the name of the relation:
    
    \begin{center}
      \begin{code}{0.8\textwidth}{}
        \small
        \BUseVerbatim{query}\pause%
      \end{code}
    \end{center}
  
    In other words, \sql{from Exercises} is understood as:
    \begin{center}
      \begin{code}{0.8\textwidth}{}
         \sql{\ \ from  Exercises Exercises}
      \end{code}    
    \end{center}
  \medskip\pause

  \item If a tuple variable is explicitly declared, e.g.:
    \begin{center}
      \begin{code}{0.8\textwidth}{}
         \sql{\ \ from  Exercises E}
      \end{code}    
    \end{center}
    then the implicit tuple variable \sql{Exercises} is \emph{not}
    declared and \sql{Exercises.number} will yield an error.
  \end{itemize}
\end{frame}