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`select()` ignores `distinct`

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
pandas, python, sql
Domain
databases

Research direction

Start by running the Python reproducer in the issue with the DuckDB table API and inspect how select("DISTINCT a, b") and distinct() build their SQL queries. The issue is done when the query includes SELECT DISTINCT a, b FROM main.foo, or when the API raises a clear exception if that form is unsupported.

Written by the indexing model from the issue text.

Description

needs triage
What happens?

select("distinct <columns>") ignores distinct.

Expected behavior: a) throw an exception if this is not supported or b) apply the distinct.

E.g. select(count("*") throws an exception _duckdb.BinderException: Binder Error: Aggregates cannot be present in a Project relation!

To Reproduce
import duckdb
import pandas as pd

df = pd.DataFrame({"a": [1, 2, 1, 1], "b": [10, 10, 10, 20], "c": [0, 1, 2, 3]})
duckdb.execute("CREATE TABLE foo AS SELECT * FROM df")

sql_query_selectdistinct = duckdb.table("foo").select("DISTINCT a, b").sql_query()

print(sql_query_selectdistinct)

assert "SELECT DISTINCT a, b FROM main.foo" == sql_query_selectdistinct
assert duckdb.table("foo").select("a, b").distinct().sql_query() == sql_query_selectdistinct

Output:

SELECT a, b FROM main.foo

Both assertions fail

OS:

Windows 11 x86_64

DuckDB Package Version:

1.4.1

Python Version:

3.13.6

Full Name:

Clemens Korner

Affiliation:

AIT Austrian Institute of Technology

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
189
Forks
117
Avg merge
1d 1h
Merged PRs (30d)
16

Getting set up

First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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