feat: Hybrid engine local join support

bigframes/core/compile/polars/compiler.py

@@ -487,8 +487,14 @@ def compile_offsets(self, node: nodes.PromoteOffsetsNode):
     def compile_join(self, node: nodes.JoinNode):
         left = self.compile_node(node.left_child)
         right = self.compile_node(node.right_child)
-        left_on = [l_name.id.sql for l_name, _ in node.conditions]
-        right_on = [r_name.id.sql for _, r_name in node.conditions]
+
+        left_on = []
+        right_on = []
+        for left_ex, right_ex in node.conditions:
+            left_ex, right_ex = lowering._coerce_comparables(left_ex, right_ex)
+            left_on.append(self.expr_compiler.compile_expression(left_ex))
+            right_on.append(self.expr_compiler.compile_expression(right_ex))
+
         if node.type == "right":
             return self._ordered_join(
                 right, left, "left", right_on, left_on, node.joins_nulls
@@ -502,8 +508,8 @@ def _ordered_join(
         left_frame: pl.LazyFrame,
         right_frame: pl.LazyFrame,
         how: Literal["inner", "outer", "left", "cross"],
-        left_on: Sequence[str],
-        right_on: Sequence[str],
+        left_on: Sequence[pl.Expr],
+        right_on: Sequence[pl.Expr],
         join_nulls: bool,
     ):
         if how == "right":

bigframes/session/polars_executor.py

@@ -37,6 +37,7 @@
     nodes.AggregateNode,
     nodes.FilterNode,
     nodes.ConcatNode,
+    nodes.JoinNode,
 )
 
 _COMPATIBLE_SCALAR_OPS = (

tests/system/small/engines/test_join.py

@@ -0,0 +1,90 @@
+# 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 typing import Literal
+
+import pytest
+
+from bigframes import operations as ops
+from bigframes.core import array_value, expression, ordering
+from bigframes.session import polars_executor
+from bigframes.testing.engine_utils import assert_equivalence_execution
+
+pytest.importorskip("polars")
+
+# Polars used as reference as its fast and local. Generally though, prefer gbq engine where they disagree.
+REFERENCE_ENGINE = polars_executor.PolarsExecutor()
+
+
+@pytest.mark.parametrize("engine", ["polars", "bq"], indirect=True)
+@pytest.mark.parametrize("join_type", ["left", "inner", "right", "outer"])
+def test_engines_join_on_key(
+    scalars_array_value: array_value.ArrayValue,
+    engine,
+    join_type: Literal["inner", "outer", "left", "right"],
+):
+    result, _ = scalars_array_value.relational_join(
+        scalars_array_value, conditions=(("int64_col", "int64_col"),), type=join_type
+    )
+
+    assert_equivalence_execution(result.node, REFERENCE_ENGINE, engine)
+
+
+@pytest.mark.parametrize("engine", ["polars", "bq"], indirect=True)
+@pytest.mark.parametrize("join_type", ["left", "inner", "right", "outer"])
+def test_engines_join_on_coerced_key(
+    scalars_array_value: array_value.ArrayValue,
+    engine,
+    join_type: Literal["inner", "outer", "left", "right"],
+):
+    result, _ = scalars_array_value.relational_join(
+        scalars_array_value, conditions=(("int64_col", "float64_col"),), type=join_type
+    )
+
+    assert_equivalence_execution(result.node, REFERENCE_ENGINE, engine)
+
+
+@pytest.mark.parametrize("engine", ["polars", "bq"], indirect=True)
+@pytest.mark.parametrize("join_type", ["left", "inner", "right", "outer"])
+def test_engines_join_multi_key(
+    scalars_array_value: array_value.ArrayValue,
+    engine,
+    join_type: Literal["inner", "outer", "left", "right"],
+):
+    l_input = scalars_array_value.order_by([ordering.ascending_over("float64_col")])
+    l_input, l_join_cols = scalars_array_value.compute_values(
+        [
+            ops.mod_op.as_expr("int64_col", expression.const(2)),
+            ops.invert_op.as_expr("bool_col"),
+        ]
+    )
+    r_input, r_join_cols = scalars_array_value.compute_values(
+        [ops.mod_op.as_expr("int64_col", expression.const(3)), expression.const(True)]
+    )
+
+    conditions = tuple((l_col, r_col) for l_col, r_col in zip(l_join_cols, r_join_cols))
+
+    result, _ = l_input.relational_join(r_input, conditions=conditions, type=join_type)
+
+    assert_equivalence_execution(result.node, REFERENCE_ENGINE, engine)
+
+
+@pytest.mark.parametrize("engine", ["polars", "bq"], indirect=True)
+def test_engines_cross_join(
+    scalars_array_value: array_value.ArrayValue,
+    engine,
+):
+    result, _ = scalars_array_value.relational_join(scalars_array_value, type="cross")
+
+    assert_equivalence_execution(result.node, REFERENCE_ENGINE, engine)