Comment 14 for bug 217644

I attempted to use the solution Michael Nelson suggested:

from storm.expr import Column
id = Column('id', tables[0])
result.count(expr=id, distinct=True)

This worked for many cases but failed when my result was a ResultSet created by the union of two intermediate ResultSets. It failed with:

ProgrammingError: missing FROM-clause entry for table "person"
   LINE 1: SELECT COUNT(DISTINCT Person.id) FROM ((SELECT Person.accoun...

This error was raised despite the fact the two intermediate ResultSets had Person in the FROM-clause.

After re-arranging my code to only issue a single query and avoid the union the above work-around worked.