\begin{frame}
  \frametitle{Having}

  \begin{alertblock}{}
    Aggregations may not be used in the \sql{where} clause.
  \end{alertblock}
  \medskip
    
  With \sql{group by}, however, it makes sense to
  \emph{filter out entire groups} based on some aggregated group
  property.
  \pause
  
  \begin{goal}{}
    This is possible with SQL's \sql{having} clause.
  \end{goal}
  
  \begin{code}{\textwidth}{}
    For example, only groups of size greater than $n$ tuples.
    \medskip
    
    \small
    \BUseVerbatim{query}
  \end{code}  

  \begin{alertblock}{}
    The condition in the \sql{having} clause may (only) involve
    aggregation functions. % and the \sql{group by} attributes.
  \end{alertblock}
\end{frame}