diff --git a/superset/charts/schemas.py b/superset/charts/schemas.py
index 225410eb4..b25f9712d 100644
--- a/superset/charts/schemas.py
+++ b/superset/charts/schemas.py
@@ -598,7 +598,10 @@ class ChartDataBoxplotOptionsSchema(ChartDataPostProcessingOperationOptionsSchem
         description="Aggregate expressions. Metrics can be passed as both "
         "references to datasource metrics (strings), or ad-hoc metrics"
         "which are defined only within the query object. See "
-        "`ChartDataAdhocMetricSchema` for the structure of ad-hoc metrics.",
+        "`ChartDataAdhocMetricSchema` for the structure of ad-hoc metrics. "
+        "When metrics is undefined or null, the query is executed without a groupby. "
+        "However, when metrics is an array (length >= 0), a groupby clause is added to "
+        "the query.",
         allow_none=True,
     )
 
diff --git a/superset/common/query_actions.py b/superset/common/query_actions.py
index 6ed18d195..ecdf00d08 100644
--- a/superset/common/query_actions.py
+++ b/superset/common/query_actions.py
@@ -140,7 +140,7 @@ def _get_samples(
     query_obj = copy.copy(query_obj)
     query_obj.is_timeseries = False
     query_obj.orderby = []
-    query_obj.metrics = []
+    query_obj.metrics = None
     query_obj.post_processing = []
     query_obj.columns = [o.column_name for o in datasource.columns]
     query_obj.from_dttm = None
diff --git a/tests/integration_tests/charts/data/api_tests.py b/tests/integration_tests/charts/data/api_tests.py
index 8d9797f67..d6ccd6aad 100644
--- a/tests/integration_tests/charts/data/api_tests.py
+++ b/tests/integration_tests/charts/data/api_tests.py
@@ -154,6 +154,7 @@ class TestPostChartDataApi(BaseTestChartDataApi):
 
         # assert
         self.assert_row_count(rv, expected_row_count)
+        assert "GROUP BY" not in rv.json["result"][0]["query"]
 
     @pytest.mark.usefixtures("load_birth_names_dashboard_with_slices")
     @mock.patch(
@@ -184,6 +185,7 @@ class TestPostChartDataApi(BaseTestChartDataApi):
 
         # assert
         self.assert_row_count(rv, expected_row_count)
+        assert "GROUP BY" not in rv.json["result"][0]["query"]
 
     @pytest.mark.usefixtures("load_birth_names_dashboard_with_slices")
     @mock.patch(
@@ -200,6 +202,7 @@ class TestPostChartDataApi(BaseTestChartDataApi):
 
         # assert
         self.assert_row_count(rv, expected_row_count)
+        assert "GROUP BY" not in rv.json["result"][0]["query"]
 
     def test_with_incorrect_result_type__400(self):
         self.query_context_payload["result_type"] = "qwerty"