The sources have been downloaded here:
http://search.cpan.org/dist/DBD-mysql/

AUTHORS
    The current version of DBD::mysql is almost completely written by
    Jochen Wiedmann, and is now being maintained by Patrick Galbraith
    (patg@mysql.com). The first version's author was Alligator
    Descartes, who was aided and abetted by Gary Shea, Andreas König
    and Tim Bunce amongst others.

    The Mysql module was originally written by Andreas König
    <koenig@kulturbox.de>. The current version, mainly an emulation
    layer, is from Jochen Wiedmann.

COPYRIGHT
    Large Portions Copyright (c) 2004-2006 MySQL Patrick Galbraith, Alexey Stroganov;
    Large Portions Copyright (c) 2003-2005 Rudolf Lippan; 
    Large Portions Copyright (c) 1997-2003 Jochen Wiedmann;
    and code portions Copyright (c)1994-1997 their original authors. 
    This module is released under the same license as Perl itself. See the
    Perl README for details.

Check the perl license in /usr/share/doc/perl/copyright.

You can also read the General Public License and the Artistic License
in /usr/share/common-licenses/GPL and /usr/share/common-licenses/Artistic
respectively.