KeyError: 'agg_1'

[juankx-bodo]

A PyDough expression using IFF with aggregates inside conditional branches raises an 'agg_1' error during SQL generation.

Error message:

Traceback (most recent call last):
  File "/home/juankx/svc/PyDough/pydough_test.py", line 182, in <module>
    sql = pydough.to_sql(unqualified_node, session=tester.session)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/juankx/svc/PyDough/pydough/evaluation/evaluate_unqualified.py", line 169, in to_sql
    return convert_relation_to_sql(relational, session, max_rows)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/juankx/svc/PyDough/pydough/sqlglot/execute_relational.py", line 88, in convert_relation_to_sql
    ).relational_to_sqlglot(relational)
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/juankx/svc/PyDough/pydough/sqlglot/sqlglot_relational_visitor.py", line 595, in relational_to_sqlglot
    root.accept(self)
  File "/home/juankx/svc/PyDough/pydough/relational/relational_nodes/relational_root.py", line 94, in accept
    visitor.visit_root(self)
  File "/home/juankx/svc/PyDough/pydough/sqlglot/sqlglot_relational_visitor.py", line 559, in visit_root
    query = self._merge_selects(
            ^^^^^^^^^^^^^^^^^^^^
  File "/home/juankx/svc/PyDough/pydough/sqlglot/sqlglot_relational_visitor.py", line 234, in _merge_selects
    new_exprs, old_exprs = self._try_merge_columns(
                           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/juankx/svc/PyDough/pydough/sqlglot/sqlglot_relational_visitor.py", line 185, in _try_merge_columns
    expr = set_glot_alias(old_column_map[new_column.this], new_name)
                          ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
KeyError: 'agg_1'

Minimal reproducible example:

## Error msg: 'agg_1'
result = TPCH.CALCULATE(
    res_is_nothing=0
).CALCULATE(
    output=IFF(res_is_nothing == 1, COUNT(customers), COUNT(suppliers)),
    #a=COUNT(customers),
    #b=COUNT(suppliers)
)

Expected result:

PyDough should generate valid SQL selecting from the active branch condition (since res_is_nothing is 0, evaluating the COUNT(suppliers) branch):

SELECT
  COUNT(*) AS output,
FROM main.supplier

Additional Context / Workarounds

The bug can be avoided if:

• res_is_nothing is set to 1, or
• Either a or b is explicitly evaluated as a standalone expression alongside output (e.g., uncommenting # a=COUNT(customers) or # b=COUNT(suppliers)).

Schema Context (TPCH Collections Used):

customers
suppliers