\begin{frame}
  \frametitle{Example Database (Students)}
  
  \begin{exampleblock}{}
    {\ttfamily
    \begin{center}
      \tableStudents
    \end{center}}
    \bigskip
    
    Meaning of the columns:
      \begin{description}\setlength{\itemindent}{0cm}
      \item [\sql{sid}:] unique number that identifies the student 
      \item [\sql{first}:] first name 
      \item [\sql{last}:] last name 
      \item [\sql{address}:] city of residence (may be null)
      \end{description}
  \end{exampleblock}
\end{frame}