Failure to collect operations that join two lazily retrieved Polars lazyframes

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#583 opened on Aug 12, 2026 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 68/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Quiet
Tech stack: python
Domain: databases

Research direction

Start at DuckDBPyRelation.pl(lazy=True) and reproduce the failure with the two relations joined through Polars, then follow the execution path into rel.join(...).collect(). Done means the supplied example collects successfully and returns the joined result without a ComputeError.

Written by the indexing model from the issue text.

Description

needs triage

What happens?

I have downstream functions that expect multiple polars.LazyFrame objects. In my upstream code, I want to source my data from DuckDB to enable efficient pushdown. However, using DuckDBPyRelation.pl(lazy=True) raises a ComputeError when operating on multiple LazyFrame objects.

To Reproduce

import duckdb

with duckdb.connect() as con:
    con.sql("CREATE TABLE tbl (t1 INTEGER)")
    con.sql("CREATE TABLE tbl2 (t1 INTEGER)")

    # Retrieve the results
    rel = con.table("tbl").pl(lazy=True)
    rel2 = con.table("tbl2").pl(lazy=True)

    # Compute and raise the error
    df = rel.join(rel2, on="t1", how="inner").collect()

the block above raises

ComputeError: caught exception during execution of a Python source, exception: InvalidInputException: Invalid Input Error: Attempting to execute an unsuccessful or closed pending query result

OS:

Linux - aarch64

DuckDB Package Version:

1.5.5

Python Version:

3.12

Full Name:

Akshay Gupta

Affiliation:

Capital One

What is the latest build you tested with? If possible, we recommend testing with the latest nightly build.

I have tested with a stable release

Did you include all relevant data sets for reproducing the issue?

Yes

Did you include all code required to reproduce the issue?

Yes, I have

Did you include all relevant configuration to reproduce the issue?

Yes, I have

Dominant language: Python
Stars: 186
Forks: 113
Avg merge: 22h 45m
Merged PRs (30d): 14

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