Remove 'partition_by' requirement from 'group_dy' method (#649)

src/datachain/func/func.py

@@ -2,7 +2,8 @@
 from collections.abc import Sequence
 from typing import TYPE_CHECKING, Any, Callable, Optional, Union
 
-from sqlalchemy import BindParameter, ColumnElement, desc
+from sqlalchemy import BindParameter, Case, ColumnElement, desc
+from sqlalchemy.ext.hybrid import Comparator
 
 from datachain.lib.convert.python_to_sql import python_to_sql
 from datachain.lib.utils import DataChainColumnError, DataChainParamsError
@@ -71,7 +72,7 @@ def _db_cols(self) -> Sequence[ColT]:
         return (
             [
                 col
-                if isinstance(col, (Func, BindParameter))
+                if isinstance(col, (Func, BindParameter, Case, Comparator))
                 else ColumnMeta.to_db_name(
                     col.name if isinstance(col, ColumnElement) else col
                 )

src/datachain/lib/dc.py

@@ -1150,7 +1150,7 @@ def select_except(self, *args: str) -> "Self":
     def group_by(
         self,
         *,
-        partition_by: Union[str, Func, Sequence[Union[str, Func]]],
+        partition_by: Optional[Union[str, Func, Sequence[Union[str, Func]]]] = None,
         **kwargs: Func,
     ) -> "Self":
         """Group rows by specified set of signals and return new signals
@@ -1167,10 +1167,10 @@ def group_by(
             )
             ```
         """
-        if isinstance(partition_by, (str, Func)):
+        if partition_by is None:
+            partition_by = []
+        elif isinstance(partition_by, (str, Func)):
             partition_by = [partition_by]
-        if not partition_by:
-            raise ValueError("At least one column should be provided for partition_by")
 
         partition_by_columns: list[Column] = []
         signal_columns: list[Column] = []

src/datachain/query/dataset.py

@@ -966,8 +966,6 @@ class SQLGroupBy(SQLClause):
     def apply_sql_clause(self, query) -> Select:
         if not self.cols:
             raise ValueError("No columns to select")
-        if not self.group_by:
-            raise ValueError("No columns to group by")
 
         subquery = query.subquery()
 

tests/unit/lib/test_datachain.py

@@ -2740,14 +2740,6 @@ def test_group_by_error(test_session):
         session=test_session,
     )
 
-    with pytest.raises(TypeError):
-        dc.group_by(cnt=func.count())
-
-    with pytest.raises(
-        ValueError, match="At least one column should be provided for partition_by"
-    ):
-        dc.group_by(cnt=func.count(), partition_by=())
-
     with pytest.raises(
         ValueError, match="At least one column should be provided for group_by"
     ):