Mac,
Here's some links to small SQL implementations:
SQLite - written in C
http://www.hwaci.com/sw/sqlite/
Gadfly - written in Python
http://gadfly.sourceforge.net
Sprite - written in Perl
http://search.cpan.org/author/TURNERJW/DBD-Sprite-0.44/lib/DBD/Sprite.pm
I don't doubt that there are others. These are the smallest ones I know of.
Cordially,
Scott