At http://www.cfsolutions.de/qb/ you will find a first beta of a visual sql query builder plugin. It is possible to drag and drop tables to the left area and to define joins between the tables via drag and drop. I have startet generating the resulting sql for mysql.
The source is not encrypted anymore. So feel free to use the source as it is.
Save and run will not work yet. Try it yourself or take a look at this YouTube Video http://www.youtube.com/watch?v=QJwlEry_ER4 to see the plugin in action.
join context menu- edit / delete join
join tooltip - show join info
agregate functions combobox
support for different database dialects / versions