\begin{frame}
  \frametitle{Natural Joins}

  \begin{code}{\textwidth}{``Natural join'' in SQL-92}
    \small
    \BUseVerbatim{query2}
  \end{code}
  Note the use of \emph{natural join}!
  \pause\bigskip
  
  DBMS to automatically add the join predicate to the query:
  \begin{tcenter}
  \begin{code}{.7\textwidth}{}
    \small\centering
    \sql{Results.category = Exercises.category \\and Results.number = Exercises.number}
  \end{code}
  \end{tcenter}

    %   SQL-92 permits joins in the \sql{from} clause as well as at the
    %   outermost query level (like \sql{union}).  This comes close to RA.
  \pause\bigskip
  
  \begin{goal}{}
    In a \emph{natural join}, the join predicate arises implicitly 
    by \emph{comparing all columns with the \alert{same name}} in both tables.
  \end{goal}
\end{frame}