maximum recursion depth exceeded / $0.key_0

[juankx-bodo]

PyDough code (without the max_recursion_depth_exceeded calculation) succeeds with pydough.explain_llm(), but fails with pydough.to_sql().

Error generating SQL:

• maximum recursion depth exceeded
• $0.key_0

Minimal reproducible example (TPCH):

# Step 1: Prepare order data with customer name and year
invoice_info = orders.CALCULATE(
    order_year=YEAR(order_date),
    key=customer.key,
    order_total=total_price
)

# Step 2: Partition by customer to calculate total per customer
customer_level = invoice_info.PARTITION(
    name="customer_groups", 
    by=(key)
).CALCULATE(
    max_recursion_depth_exceeded=SUM(invoice_info.order_total),
    key_0_error=SUM(orders.total_price)
)

Additional Context / Workarounds

Behavior Shift: Removing the max_recursion_depth_exceeded calculation produces a $0.key_0 error instead, and pydough.explain_llm() succeeds at this point.
Workaround: The bug can be prevented by changing key=customer.key to cust_id=customer.key in Step 1.

TPCH collections used:

  orders
  ├── order_date
  ├── total_price
  └── customer [one member of customers]

  customers
  ├── key
  └── orders [multiple orders]

[juankx-bodo]

Minimal reproducible example (TPCH):

info = orders.CALCULATE(
    key=customer.key,   # explicit ancestor reference
    year=YEAR(order_date)
)
partition_error = info.PARTITION(
    name="yearly_groups", by=(key)
).CALCULATE(
    max_recursion_depth_exceeded=SUM(info.order_total),
    key_0_error=SUM(orders.total_price)
)

• maximum recursion depth exceeded if max_recursion_depth_exceeded is included in the last CALCULATE
• $0.key_0 if key_0_error is included