\begin{frame} \frametitle{The From Clause} % \structureExercises \begin{goal}{} For each table in the \sql{from} clause there is a tuple variable. \end{goal} \begin{itemize} \pause \item If the the name of the tuple variable is not given explicitly, the variable will have the name of the relation: \begin{center} \begin{code}{0.8\textwidth}{} \small \BUseVerbatim{query}\pause% \end{code} \end{center} In other words, \sql{from Exercises} is understood as: \begin{center} \begin{code}{0.8\textwidth}{} \sql{\ \ from Exercises Exercises} \end{code} \end{center} \medskip\pause \item If a tuple variable is explicitly declared, e.g.: \begin{center} \begin{code}{0.8\textwidth}{} \sql{\ \ from Exercises E} \end{code} \end{center} then the implicit tuple variable \sql{Exercises} is \emph{not} declared and \sql{Exercises.number} will yield an error. \end{itemize} \end{frame}