\begin{frame}
  \frametitle{Not In}
  
  \begin{block}{}
    With 
    \begin{itemize}
      \item \sql{in} 
      \item \sql{not in} 
    \end{itemize}  
    it is possible to check whether an attribute value appears in a set of
    values computed by another SQL \emph{subquery.}
  \end{block}
  \medskip
  
  \begin{code}{\textwidth}{Students without any homework result}
    \small
    \BUseVerbatim{query}
  \end{code}
  \vspace{-1ex}
    
  \footnotesize\ttfamily\centering
  \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{frame}