sql.py: mk_select(): joins: Switched to using filter_out as an attribute of the Join object instead of a sentinel value for the first column. Filter by the right table's pkey being NULL instead of each joined column being NULL, because some joined columns may contain NULL values which would mess things up, but the pkey presumably is NOT NULL.
sql.py: mk_select(): joins: Switched to using filter_out as an attribute of the Join object instead of a sentinel value for the first column. Filter by the right table's pkey being NULL instead of each joined column being NULL, because some joined columns may contain NULL values which would mess things up, but the pkey presumably is NOT NULL.