I had a really good answer to my question Using CASE to select between two geometry functions? but a problem arises if there are more than one lake in a forest; then the solution returns multiple forests.
Let me rephrase the question in much more general terms.
I have some forest polygons, and some lake polygons, in separate tables (layers) in PostgreSQL. I want to use PostGIS/PostgreSQL to create a new table with forests, that have holes where the lakes are.
Some forests have many lakes, some have one, and many have none. I expect the number of output forests to be the same as the input forests (except if a forest is actually cut entirely by a lake).
I need to preserve an ID-number attribute on the forests.