\begin{frame}
  \frametitle{Joins}
  
  Up to version SQL-86, there were no explicit joins in queries.
  Instead, Cartesian products of relations filtered via \sql{where}.
  \bigskip
      
  \begin{code}{\textwidth}{}
    \small
    \BUseVerbatim{query}
  \end{code}
  \pause\smallskip
  
  \begin{goal}{}
    Since SQL-92 there are explicit join operations.
  \end{goal}
\end{frame}