How to put content from multiple databases in one table using datatool?

datatool-01.tex

%% https://tex.stackexchange.com/questions/117747/how-to-put-content-from-multiple-databases-in-one-table-using-datatool

\documentclass{article}

\usepackage{datatool}

% generate first test database
\begin{filecontents}{first.csv}
Year,Number
2001,10
2002,20
2003,30
2004,40
\end{filecontents}

% generate second test database
\begin{filecontents}{second.csv}
Year,Number
2001,101
2002,202
2003,303
2004,404
\end{filecontents}

\DTLloaddb{first}{first.csv}
\DTLloaddb{second}{second.csv}

\begin{document}

% append second column of second data base to first data base

\newcount\rowIdx

\dtlforcolumn{\secondNumber}{second}{Number}%
{%
  % iterate through each entry in the `Number' column of the second database
  \advance\rowIdx by 1\relax
  % get corresponding row of first database
  \dtlgetrow{first}{\rowIdx}%
  % append to current row (this new column is assigned the key `Number2')
  \dtlappendentrytocurrentrow{Number2}{\secondNumber}%
  % update first database
  \dtlrecombine
}

\DTLdisplaydb{first}

\end{document}