\begin{frame}
  \frametitle{Not Exists}

  \query
  
  \begin{center}
    \tableSmall
    \colorbox{rellight}{%
      \begin{tabular}[t]{|r|r|}
        \multicolumn{2}{c}{Query Result} \\ \hline
        \hd{first} & \hd{last} \\ \hline
        Bart & Simpson \\ 
        George & Washington \\
        \hline
      \end{tabular}%
    }%
  \end{center}
  \pause

  \begin{goal}{Conceptually \ldots}
    Tuple variable \sql{S} loops over the 5 rows in \sql{Students}.
    \medskip
    
    The subquery is evaluated 5 times.    
  \end{goal}
  \remark{%
    The DBMS is free to choose a more efficient equivalent
    evaluation strategy (for instance,\ query unnesting).
  }
  \vspace{10cm}
\end{frame}