PostgreSQL schemas, select same table from all schemas
This might be a good case for using table inheritance.  Create the initial table in the master schema and then make all user tables inherit it.

The key to making this work well is to see the master table as as abstract mixin rather than a typical public class inheritance.  The parent table then gives you, essentially, a catalog of all child tables' contents.   This becomes problematic if you also insert into the parent table so you may want to use a trigger to avoid that.