GridMonger supports table joins to only a limited degree at present.

The 'main' table is the displayed data. A 'joined' table can be added that will affect the records displayed.  The join is a part of the WHERE clause and not a part of the data displayed.

For example, a table of motor vehicles located in various U.S. states can be queried, with the results limited to those located only in California by querying a second, related table and pulling the state of residency. 

See the Live Demos page for an example of this in action using a table of U.S. states and a separate one containing U.S. ZIP codes (you'll need to download the application to see how it is set up).