\begin{frame}
  \frametitle{Excluding Null Values}

  \begin{goal}{}
    Since null values may lead to complications, 
    SQL allows to control whether an attribute value may be null or not.    
  \end{goal}
  By default, null values are allowed.
  \bigskip

  \begin{code}{\textwidth}{}
    \small
    \BUseVerbatim{notnull}
  \end{code}
  \vspace{-1ex}
  
  Declaring attributes as \sql{not null} leads to 
  \begin{itemize}
    \item simpler application programs, and
    \item fewer surprises during query evaluation.
  \end{itemize}
\end{frame}

% \overview{3}
\theme{Integrity Constraints}