\begin{frame} \frametitle{Restrictions} \emph{The following are not allowed:} \begin{itemize} \medskip \item Simple aggregations may not be nested (makes no sense): \begin{code}{0.8\textwidth}{\small\bfseries Wrong!} \small $\quad\cdots$ \sql{sum(avg(A))} $\cdots$ \end{code} \pause\medskip \item Aggregations may not be used in the \sql{where} clause: \smallskip \begin{code}{0.8\textwidth}{\small\bfseries Wrong!} \small $\quad\cdots$ \sql{where sum(A) > 100} $\cdots$ \end{code} \pause\medskip \item If an aggregation function is used without \sql{group by}, \\ \emph{no attributes} may appear in the \sql{select} clause: \smallskip \begin{code}{0.8\textwidth}{\small Wrong!} \small \BUseVerbatim{query} \end{code} \end{itemize} \end{frame}