[postgis-users] Combining squares

[Brian Peschel]

I have an unusual problem I was wondering if there is way for PostGIS to 
solve for me.

I have squares.  A lot of squares.  Thousands of squares.  I would love 
to combine them into one or more larger polygons.  But, they must valid 
polygons, non-reentrant.  For example. if you have a 3x3 grid of squares,
ABC
RST
XYZ
and I want to combine all but the center, I would need either 2 polygons 
(something like ABC and RXYZT), or one polygon with an inner ring.

Does this make sense?  Anyone done something like this, with or without 
PostGIS?

- Brian