fix: duckdb Lazyframe.unique was raising when column name was "group" (#3070)

Author: MarcoGorelli

narwhals/_duckdb/dataframe.py

@@ -13,6 +13,7 @@
     catch_duckdb_exception,
     col,
     evaluate_exprs,
+    join_column_names,
     lit,
     native_to_narwhals_dtype,
     window_expression,
@@ -396,7 +397,7 @@ def unique(
                 .filter(col(name) == lit(1))
                 .select(StarExpression(exclude=[count_name, idx_name]))
             )
-        return self._with_native(self.native.unique(", ".join(self.columns)))
+        return self._with_native(self.native.unique(join_column_names(*self.columns)))
 
     def sort(self, *by: str, descending: bool | Sequence[bool], nulls_last: bool) -> Self:
         if isinstance(descending, bool):
@@ -499,16 +500,16 @@ def unpivot(
             msg = "`value_name` cannot be empty string for duckdb backend."
             raise NotImplementedError(msg)
 
-        unpivot_on = ", ".join(str(col(name)) for name in on_)
+        unpivot_on = join_column_names(*on_)
         rel = self.native  # noqa: F841
         # Replace with Python API once
         # https://github.com/duckdb/duckdb/discussions/16980 is addressed.
         query = f"""
             unpivot rel
             on {unpivot_on}
             into
-                name "{variable_name}"
-                value "{value_name}"
+                name {col(variable_name)}
+                value {col(value_name)}
             """
         return self._with_native(
             duckdb.sql(query).select(*[*index_, variable_name, value_name])

narwhals/_duckdb/utils.py

@@ -295,6 +295,10 @@ def generate_partition_by_sql(*partition_by: str | Expression) -> str:
     return f"partition by {by_sql}"
 
 
+def join_column_names(*names: str) -> str:
+    return ", ".join(str(col(name)) for name in names)
+
+
 def generate_order_by_sql(
     *order_by: str | Expression, descending: Sequence[bool], nulls_last: Sequence[bool]
 ) -> str:

tests/frame/unique_test.py

@@ -4,8 +4,6 @@
 
 import pytest
 
-# We use nw instead of nw.stable.v1 to ensure that DuckDBPyRelation
-# becomes LazyFrame instead of DataFrame
 import narwhals as nw
 from narwhals.exceptions import ColumnNotFoundError
 from tests.utils import DUCKDB_VERSION, Constructor, ConstructorEager, assert_equal_data
@@ -100,3 +98,15 @@ def test_unique_none(constructor: Constructor) -> None:
     if not isinstance(df, nw.LazyFrame):
         result = df.unique(maintain_order=True)
         assert_equal_data(result, data)
+
+
+def test_unique_3069(constructor: Constructor, request: pytest.FixtureRequest) -> None:
+    if "ibis" in str(constructor):
+        # https://github.com/ibis-project/ibis/issues/11591
+        request.applymarker(pytest.mark.xfail)
+    data = {"name": ["a", "b", "c"], "group": ["d", "e", "f"], "value": [1, 2, 3]}
+    df = nw.from_native(constructor(data))
+    unique_to_get = "group"
+    result = df.select(nw.col(unique_to_get)).unique().sort(unique_to_get)
+    expected = {"group": ["d", "e", "f"]}
+    assert_equal_data(result, expected)