\begin{frame} \frametitle{Conditional Expressions} A typical application is to \emph{replace a null value} by a value $Y$: \smallskip \begin{code}{\textwidth}{} \small \quad\sql{$\cdots$ case when $X$ is not null then $X$ else $Y$ end $\cdots$} \end{code} \pause\medskip In SQL-92, this may be abbreviated to \begin{code}{\textwidth}{} \small \quad\sql{$\cdots$ coalesce ($X$, $Y$)$\cdots$} \end{code} \medskip \begin{code}{\textwidth}{List the addresses of all students} \small \BUseVerbatim{query} \end{code} \end{frame}