\begin{frame} \frametitle{Inner and Outer Joins} \structureAll \begin{code}{\textwidth}{Number of submission per homework (0 if no submission)} \small \BUseVerbatim{query} \end{code} \pause\smallskip All Exercises are present in the result of the left (outer) join. \begin{itemize} \item for exercises without solutions, \sql{sid} and \sql{points} will be \sql{null} \item \sql{count(sid)} ignores rows where \sql{sid is null}. \end{itemize} \pause\medskip Could also be solved using \emph{union}, but less elegant (longer). \end{frame}