\begin{frame}[t]
  \frametitle{Exercise}
  
  \structureAll
  \medskip
  
  \begin{quiz}{0.95\textwidth}{Formulate the following query in SQL}
    The topics of all exercises solved by George Orwell?
  \end{quiz}
  \bigskip

  The \emph{connection graph} with foreign key relations:
  \begin{center}
    \begin{tikzpicture}[n/.style={rectangle,rounded corners=1mm,draw=black,fill=cblue!30,inner sep=1mm}]
      \node (S) [n] {\sql{Students}};
      \node (R) [n,right of=S,node distance=35mm] {\sql{Results}};
      \node (E) [n,right of=R,node distance=35mm] {\sql{Exercises}};
      \draw (S) to node [below,align=center] {} (R);
      \draw (R) to node [below,align=center] {} (E);
    \end{tikzpicture}\vspace{-1ex}
  \end{center}
  \pause
  We establish the link via a tuple variable \sql{R} over \sql{Results}:
  \begin{tcenter}
  \begin{code}{\textwidth}{}
    \small
    \BUseVerbatim{query}
  \end{code}
  \end{tcenter}  
\end{frame}