\begin{frame} \frametitle{Primary Keys} \begin{center} {\small\ttfamily \colorbox{rellight}{% \begin{tabular}[t]{|r|r|r|r|r|} \multicolumn{5}{c}{Customer} \\ \hline \hd{first-name} & \hd{last-name} & \hd{phone} & \hd{street} & \hd{city} \\ \hline Tom & James & 06-73917384 & Main & London \\ Joe & Jones & 06-18384405 & Slater & Paris \\ \hline \end{tabular}% }} \end{center} \begin{alertblock}{} What would be a good primary key? \end{alertblock} \medskip \pause Is \ $\{\;\textit{first-name},\;\textit{last-name},\;\textit{phone}\;\}$ a good key? \pause \begin{itemize} \item the phone number can change \item is it really unique? \end{itemize} \medskip \pause \begin{goal}{} It is often good to introduce an artificial \emph{internal key}: \begin{itemize} \item e.g. \textit{customer-id} \item \emph{advantage: unique, does not change} \item minor disadvantage: no descriptive meaning \end{itemize} \end{goal} \bigskip\bigskip \end{frame}