\begin{frame}
  \frametitle{Not Exists}

  \query

  \begin{goal}{}
    Finally, \sql{S} is the \sql{Students} tuple
      \begin{tcenter}
        \raisebox{-1ex}{\colorbox{rellight}{%
          \footnotesize\ttfamily
          \begin{tabular}{|r|r|r|r|}
            \hline
            \hd{sid} & \hd{first} & \hd{last} & \hd{address} \\
            \hline
            105 & George & Washington & null \\
            \hline
          \end{tabular}%
        }}\pause\vspace{1ex}
      \end{tcenter}
    In the subquery, \sql{S.sid} is instantiated by \sql{105}:\\[1ex]
      ~~\begin{minipage}{.5\textwidth}%
        \footnotesize\ttfamily%
        $
        \begin{array}{ll}
          \sql{select} & \sql{*} \\
          \sql{from}   & \sql{Results R} \\
          \sql{where}  & \sql{R.category = \textquotesingle{}homework\textquotesingle{}} \\
          \sql{and}    & \sql{R.sid = {\setlength{\fboxsep}{2pt}\fbox{105}}}
        \end{array}
        $
      \end{minipage}
      \begin{minipage}{.4\textwidth}
        \tableTiny
        \colorbox{rellight}{%
          \begin{tabular}[t]{|r|r|r|r|}
            \multicolumn{4}{c}{Query Result} \\ \hline
            \hd{sid} & \hd{category} & \hd{number} & \hd{points} \\ \hline
            \multicolumn{4}{|c|}{\normalfont (no rows selected)} \\
            \hline
          \end{tabular}%
        }
      \end{minipage}\\[1ex]\pause
    The result is empty. So the \sql{not exists} is true for \emph{this} \sql{S}.
  \end{goal}
  \vspace{10cm}
\end{frame}