https://github.com/chanhong/pdolite
Very lite PDO database class with lite query builder and SIDU (Select, Insert, Delete, Update). One class file with the size of 22 KB.
You can also use all the native PDO methods: http://php.net/manual/en/book.pdo.php
Installation
$ ./composer.phar require chanhong/pdolite 1.0.x-dev