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\begin{frame}[fragile] \frametitle{Multiple Tables} \begin{goal}{} \emph{Query:} PIDs of all people that have chatted with everyone in the persons table (except themselves). \end{goal} \begin{exampleblock}{SQL Query} {\small \begin{verbatim}SELECT Y.PID FROM Person as Y WHERE NOT EXISTS ( SELECT * FROM Person as X WHERE Y.PID != X.PID AND NOT EXISTS ( SELECT * FROM Chats as C WHERE ( C.P1 = Y.PID AND C.P2 = X.PID ) OR ( C.P1 = X.PID AND C.P2 = Y.PID ) ) )\end{verbatim}% } \end{exampleblock} There is no FORALL in SQL. Recall $\myall{x}{\phi(x)} \equiv \neg\myex{x}{\neg{\phi(x)}}$ ! \end{frame}