BUG: pivot_table with margins=T raises when results in empty df (pandas-dev#49438)

* BUG: pivot_table with margins=T raises when results in empty df

* suggested change

* suggested change

* Update pivot.py

* linked test to issue

* suggested edit

Author: debnathshoham

doc/source/whatsnew/v2.0.0.rst

@@ -456,7 +456,7 @@ Reshaping
 - Bug in :meth:`DataFrame.unstack` and :meth:`Series.unstack` unstacking wrong level of :class:`MultiIndex` when :class:`MultiIndex` has mixed names (:issue:`48763`)
 - Bug in :meth:`DataFrame.pivot` not respecting ``None`` as column name (:issue:`48293`)
 - Bug in :func:`join` when ``left_on`` or ``right_on`` is or includes a :class:`CategoricalIndex` incorrectly raising ``AttributeError`` (:issue:`48464`)
--
+- Bug in :meth:`DataFrame.pivot_table` raising ``ValueError`` with parameter ``margins=True`` when result is an empty :class:`DataFrame` (:issue:`49240`)
 
 Sparse
 ^^^^^^

pandas/core/reshape/pivot.py

@@ -411,7 +411,11 @@ def _all_key(key):
                 table_pieces.append(transformed_piece)
                 margin_keys.append(all_key)
 
-        result = concat(table_pieces, axis=cat_axis)
+        if not table_pieces:
+            # GH 49240
+            return table
+        else:
+            result = concat(table_pieces, axis=cat_axis)
 
         if len(rows) == 0:
             return result

pandas/tests/reshape/test_pivot.py

@@ -2086,8 +2086,9 @@ def test_pivot_table_aggfunc_scalar_dropna(self, dropna):
 
         tm.assert_frame_equal(result, expected)
 
-    def test_pivot_table_empty_aggfunc(self):
-        # GH 9186 & GH 13483
+    @pytest.mark.parametrize("margins", [True, False])
+    def test_pivot_table_empty_aggfunc(self, margins):
+        # GH 9186 & GH 13483 & GH 49240
         df = DataFrame(
             {
                 "A": [2, 2, 3, 3, 2],
@@ -2096,7 +2097,9 @@ def test_pivot_table_empty_aggfunc(self):
                 "D": [None, None, None, None, None],
             }
         )
-        result = df.pivot_table(index="A", columns="D", values="id", aggfunc=np.size)
+        result = df.pivot_table(
+            index="A", columns="D", values="id", aggfunc=np.size, margins=margins
+        )
         expected = DataFrame(index=Index([], dtype="int64", name="A"))
         expected.columns.name = "D"
         tm.assert_frame_equal(result, expected)