\begin{frame}
  \frametitle{Not In}

  \begin{itemize}
  \item In SQL-86,\\ subquery is required to deliver a \emph{single output column}
  \bigskip
  
  \item In SQL-92,\\
    comparisons where extended to the tuple level.  
    \medskip
    
    It is thus valid to write, e.g.:
    
    {\centering
      \begin{code}{0.9\textwidth}{}
        \small\centering
        $
        \begin{array}{c}
          \vdots \\
          \sql{where (A,B) not in (select C,D from \dots)}
        \end{array}
        $
      \end{code}
      
    }  
  \end{itemize}
\end{frame}