refactor: add apply_window_if_present and get_window_order_by methods

bigframes/core/compile/sqlglot/aggregations/nullary_compiler.py

@@ -20,7 +20,7 @@
 
 from bigframes.core import window_spec
 import bigframes.core.compile.sqlglot.aggregations.op_registration as reg
-from bigframes.core.compile.sqlglot.aggregations.utils import apply_window_if_present
+from bigframes.core.compile.sqlglot.aggregations.windows import apply_window_if_present
 from bigframes.operations import aggregations as agg_ops
 
 NULLARY_OP_REGISTRATION = reg.OpRegistration()

bigframes/core/compile/sqlglot/aggregations/unary_compiler.py

@@ -20,7 +20,7 @@
 
 from bigframes.core import window_spec
 import bigframes.core.compile.sqlglot.aggregations.op_registration as reg
-from bigframes.core.compile.sqlglot.aggregations.utils import apply_window_if_present
+from bigframes.core.compile.sqlglot.aggregations.windows import apply_window_if_present
 import bigframes.core.compile.sqlglot.expressions.typed_expr as typed_expr
 import bigframes.core.compile.sqlglot.sqlglot_ir as ir
 from bigframes.operations import aggregations as agg_ops

bigframes/core/compile/sqlglot/aggregations/windows.py

@@ -0,0 +1,153 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from __future__ import annotations
+
+import typing
+
+import sqlglot.expressions as sge
+
+from bigframes.core import utils, window_spec
+import bigframes.core.compile.sqlglot.scalar_compiler as scalar_compiler
+import bigframes.core.ordering as ordering_spec
+
+
+def apply_window_if_present(
+    value: sge.Expression,
+    window: typing.Optional[window_spec.WindowSpec] = None,
+) -> sge.Expression:
+    if window is None:
+        return value
+
+    if window.is_row_bounded and not window.ordering:
+        raise ValueError("No ordering provided for ordered analytic function")
+    elif (
+        not window.is_row_bounded
+        and not window.is_range_bounded
+        and not window.ordering
+    ):
+        # Unbound grouping window.
+        order_by = None
+    elif window.is_range_bounded:
+        # Note that, when the window is range-bounded, we only need one ordering key.
+        # There are two reasons:
+        # 1. Manipulating null positions requires more than one ordering key, which
+        #  is forbidden by SQL window syntax for range rolling.
+        # 2. Pandas does not allow range rolling on timeseries with nulls.
+        order_by = get_window_order_by((window.ordering[0],), override_null_order=False)
+    else:
+        order_by = get_window_order_by(window.ordering, override_null_order=True)
+
+    order = sge.Order(expressions=order_by) if order_by else None
+
+    group_by = (
+        [scalar_compiler.compile_scalar_expression(key) for key in window.grouping_keys]
+        if window.grouping_keys
+        else None
+    )
+
+    # This is the key change. Don't create a spec for the default window frame
+    # if there's no ordering. This avoids generating an `ORDER BY NULL` clause.
+    if not window.bounds and not order:
+        return sge.Window(this=value, partition_by=group_by)
+
+    kind = (
+        "ROWS" if isinstance(window.bounds, window_spec.RowsWindowBounds) else "RANGE"
+    )
+
+    start: typing.Union[int, float, None] = None
+    end: typing.Union[int, float, None] = None
+    if isinstance(window.bounds, window_spec.RangeWindowBounds):
+        if window.bounds.start is not None:
+            start = utils.timedelta_to_micros(window.bounds.start)
+        if window.bounds.end is not None:
+            end = utils.timedelta_to_micros(window.bounds.end)
+    elif window.bounds:
+        start = window.bounds.start
+        end = window.bounds.end
+
+    start_value, start_side = _get_window_bounds(start, is_preceding=True)
+    end_value, end_side = _get_window_bounds(end, is_preceding=False)
+
+    spec = sge.WindowSpec(
+        kind=kind,
+        start=start_value,
+        start_side=start_side,
+        end=end_value,
+        end_side=end_side,
+        over="OVER",
+    )
+
+    return sge.Window(this=value, partition_by=group_by, order=order, spec=spec)
+
+
+def get_window_order_by(
+    ordering: typing.Tuple[ordering_spec.OrderingExpression, ...],
+    override_null_order: bool = False,
+) -> typing.Optional[tuple[sge.Ordered, ...]]:
+    """Returns the SQL order by clause for a window specification."""
+    if not ordering:
+        return None
+
+    order_by = []
+    for ordering_spec_item in ordering:
+        expr = scalar_compiler.compile_scalar_expression(
+            ordering_spec_item.scalar_expression
+        )
+        desc = not ordering_spec_item.direction.is_ascending
+        nulls_first = not ordering_spec_item.na_last
+
+        if override_null_order:
+            # Bigquery SQL considers NULLS to be "smallest" values, but we need
+            # to override in these cases.
+            is_null_expr = sge.Is(this=expr, expression=sge.Null())
+            if nulls_first and desc:
+                order_by.append(
+                    sge.Ordered(
+                        this=is_null_expr,
+                        desc=desc,
+                        nulls_first=nulls_first,
+                    )
+                )
+            elif not nulls_first and not desc:
+                order_by.append(
+                    sge.Ordered(
+                        this=is_null_expr,
+                        desc=desc,
+                        nulls_first=nulls_first,
+                    )
+                )
+
+        order_by.append(
+            sge.Ordered(
+                this=expr,
+                desc=desc,
+                nulls_first=nulls_first,
+            )
+        )
+    return tuple(order_by)
+
+
+def _get_window_bounds(
+    value, is_preceding: bool
+) -> tuple[typing.Union[str, sge.Expression], typing.Optional[str]]:
+    """Compiles a single boundary value into its SQL components."""
+    if value is None:
+        side = "PRECEDING" if is_preceding else "FOLLOWING"
+        return "UNBOUNDED", side
+
+    if value == 0:
+        return "CURRENT ROW", None
+
+    side = "PRECEDING" if value < 0 else "FOLLOWING"
+    return sge.convert(abs(value)), side

bigframes/core/compile/sqlglot/compiler.py

@@ -23,6 +23,7 @@
 from bigframes.core import expression, guid, identifiers, nodes, pyarrow_utils, rewrite
 from bigframes.core.compile import configs
 import bigframes.core.compile.sqlglot.aggregate_compiler as aggregate_compiler
+from bigframes.core.compile.sqlglot.aggregations import windows
 from bigframes.core.compile.sqlglot.expressions import typed_expr
 import bigframes.core.compile.sqlglot.scalar_compiler as scalar_compiler
 import bigframes.core.compile.sqlglot.sqlglot_ir as ir
@@ -272,18 +273,16 @@ def compile_random_sample(
     def compile_aggregate(
         self, node: nodes.AggregateNode, child: ir.SQLGlotIR
     ) -> ir.SQLGlotIR:
-        ordering_cols = tuple(
-            sge.Ordered(
-                this=scalar_compiler.compile_scalar_expression(
-                    ordering.scalar_expression
-                ),
-                desc=ordering.direction.is_ascending is False,
-                nulls_first=ordering.na_last is False,
-            )
-            for ordering in node.order_by
+        ordering_cols = windows.get_window_order_by(
+            node.order_by, override_null_order=True
         )
         aggregations: tuple[tuple[str, sge.Expression], ...] = tuple(
-            (id.sql, aggregate_compiler.compile_aggregate(agg, order_by=ordering_cols))
+            (
+                id.sql,
+                aggregate_compiler.compile_aggregate(
+                    agg, order_by=ordering_cols if ordering_cols else ()
+                ),
+            )
             for agg, id in node.aggregations
         )
         by_cols: tuple[sge.Expression, ...] = tuple(

tests/unit/core/compile/sqlglot/aggregations/test_windows.py

@@ -0,0 +1,141 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+
+import pandas as pd
+import pytest
+import sqlglot.expressions as sge
+
+from bigframes.core import window_spec
+from bigframes.core.compile.sqlglot.aggregations.windows import (
+    apply_window_if_present,
+    get_window_order_by,
+)
+import bigframes.core.expression as ex
+import bigframes.core.ordering as ordering
+
+
+class WindowsTest(unittest.TestCase):
+    def test_get_window_order_by_empty(self):
+        self.assertIsNone(get_window_order_by(tuple()))
+
+    def test_get_window_order_by(self):
+        result = get_window_order_by((ordering.OrderingExpression(ex.deref("col1")),))
+        self.assertEqual(
+            sge.Order(expressions=result).sql(dialect="bigquery"),
+            "ORDER BY `col1` ASC NULLS LAST",
+        )
+
+    def test_get_window_order_by_override_nulls(self):
+        result = get_window_order_by(
+            (ordering.OrderingExpression(ex.deref("col1")),),
+            override_null_order=True,
+        )
+        self.assertEqual(
+            sge.Order(expressions=result).sql(dialect="bigquery"),
+            "ORDER BY `col1` IS NULL ASC NULLS LAST, `col1` ASC NULLS LAST",
+        )
+
+    def test_get_window_order_by_override_nulls_desc(self):
+        result = get_window_order_by(
+            (
+                ordering.OrderingExpression(
+                    ex.deref("col1"),
+                    direction=ordering.OrderingDirection.DESC,
+                    na_last=False,
+                ),
+            ),
+            override_null_order=True,
+        )
+        self.assertEqual(
+            sge.Order(expressions=result).sql(dialect="bigquery"),
+            "ORDER BY `col1` IS NULL DESC NULLS FIRST, `col1` DESC NULLS FIRST",
+        )
+
+    def test_apply_window_if_present_no_window(self):
+        value = sge.func(
+            "SUM", sge.Column(this=sge.to_identifier("col_0", quoted=True))
+        )
+        result = apply_window_if_present(value)
+        self.assertEqual(result, value)
+
+    def test_apply_window_if_present_row_bounded_no_ordering_raises(self):
+        with pytest.raises(
+            ValueError, match="No ordering provided for ordered analytic function"
+        ):
+            apply_window_if_present(
+                sge.Var(this="value"),
+                window_spec.WindowSpec(
+                    bounds=window_spec.RowsWindowBounds(start=-1, end=1)
+                ),
+            )
+
+    def test_apply_window_if_present_unbounded_grouping_no_ordering(self):
+        result = apply_window_if_present(
+            sge.Var(this="value"),
+            window_spec.WindowSpec(
+                grouping_keys=(ex.deref("col1"),),
+            ),
+        )
+        self.assertEqual(
+            result.sql(dialect="bigquery"),
+            "value OVER (PARTITION BY `col1`)",
+        )
+
+    def test_apply_window_if_present_range_bounded(self):
+        result = apply_window_if_present(
+            sge.Var(this="value"),
+            window_spec.WindowSpec(
+                ordering=(ordering.OrderingExpression(ex.deref("col1")),),
+                bounds=window_spec.RangeWindowBounds(start=None, end=pd.Timedelta(0)),
+            ),
+        )
+        self.assertEqual(
+            result.sql(dialect="bigquery"),
+            "value OVER (ORDER BY `col1` ASC NULLS LAST RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)",
+        )
+
+    def test_apply_window_if_present_range_bounded_timedelta(self):
+        result = apply_window_if_present(
+            sge.Var(this="value"),
+            window_spec.WindowSpec(
+                ordering=(ordering.OrderingExpression(ex.deref("col1")),),
+                bounds=window_spec.RangeWindowBounds(
+                    start=pd.Timedelta(days=-1), end=pd.Timedelta(hours=12)
+                ),
+            ),
+        )
+        self.assertEqual(
+            result.sql(dialect="bigquery"),
+            "value OVER (ORDER BY `col1` ASC NULLS LAST RANGE BETWEEN 86400000000 PRECEDING AND 43200000000 FOLLOWING)",
+        )
+
+    def test_apply_window_if_present_all_params(self):
+        result = apply_window_if_present(
+            sge.Var(this="value"),
+            window_spec.WindowSpec(
+                grouping_keys=(ex.deref("col1"),),
+                ordering=(ordering.OrderingExpression(ex.deref("col2")),),
+                bounds=window_spec.RowsWindowBounds(start=-1, end=0),
+            ),
+        )
+        self.assertEqual(
+            result.sql(dialect="bigquery"),
+            "value OVER (PARTITION BY `col1` ORDER BY `col2` IS NULL ASC NULLS LAST, `col2` ASC NULLS LAST ROWS BETWEEN 1 PRECEDING AND CURRENT ROW)",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()