Have you heard of Adminer (http://www.adminer.org/)?
"It consist of a single file ready to deploy to the target server. Adminer is available for MySQL, PostgreSQL, SQLite, MS SQL and Oracle."
As I see its development consists of several files and a separate section for database drivers (http://adminer.svn.sourceforge.net/viewvc/adminer/branches/sqlite/adminer/drivers/). Later it is "compiled" into a single file script which can be uploaded later to the server. I tried it and it runs really fast. It also has some kind of AJAX in the code as well.
For your information, Adminer ranked in SF.net on 21st place. Daily 300~400 downloads. I checked the sample MySQL driver file. It consists of about 700 lines of code.
What do you think about it?
Yes, it looks interesting!
Let me take a look these days.