"Quine:" a program that outputs it's complete source code when run.
I was lounging around in the MySQL chat room on irc.freenode.net, and someone suggested that I try to write a MySQL quine - a database query that would return the text of the query itself.
After about half an hour of screwing around, I got it! It may not be a fantastic achievement, but I feel pretty leet about writing my first quine in a database query language.
SELECT REPLACE(@v:='SELECT REPLACE(@v:=\'2\',1+1,REPLACE(REPLACE(@v,\'\\\\\',\'\\\\\\\\\'),\'\\\'\',\'\\\\\\\'\'));',1+1,REPLACE(REPLACE(@v,'\\','\\\\'),'\'','\\\''));
Only 167 characters. Hah!