Parallel overlays in Beamer

Question

I have 2 columns of blocks side by side in 1 slide:

\begin{columns}
  \begin{column}{0.48\textwidth}
    \begin{block}{left block 1}
      left block 1
    \end{block}
    \begin{block}{left block 2}
      left block 2
    \end{block}
  \end{column}
  \begin{column}{0.48\textwidth}
    \begin{block}{right block 1}
      right block 1
    \end{block}
    \begin{block}{right block 2}
      right block 2
    \end{block}
  \end{column}
\end{columns}

What I would like to realize is: left block 1 and right block 1 are shown initially, when I left-click the mouse, left block 2 and right block 2 are shown at the same time under them.

I don't know if it is possible to do it by onslide or pause... Could anyone help?

Answer 1

Just add overlay specifications to the lower blocks, as in:

\documentclass{beamer}
\begin{document}
\begin{frame}
\begin{columns}
  \begin{column}{0.48\textwidth}
    \begin{block}{left block 1}
      left block 1
    \end{block}
    \begin{block}<2>{left block 2}
      left block 2
    \end{block}
  \end{column}
  \begin{column}{0.48\textwidth}
    \begin{block}{right block 1}
      right block 1
    \end{block}
    \begin{block}<2>{right block 2}
      right block 2
    \end{block}
  \end{column}
\end{columns}
\end{frame}
\end{document}