BUG: Pandas throws exception if Google Bigquery output is empty, #10274

Author: Saumitra Shahapure

doc/source/whatsnew/v0.17.0.txt

@@ -815,3 +815,4 @@ Bug Fixes
 - Bug preventing access to the first index when using ``iloc`` with a list containing the appropriate negative integer (:issue:`10547`, :issue:`10779`)
 - Bug in ``TimedeltaIndex`` formatter causing error while trying to save ``DataFrame`` with ``TimedeltaIndex`` using ``to_csv`` (:issue:`10833`)
 - Bug in ``DataFrame.where`` when handling Series slicing (:issue:`10218`, :issue:`9558`)
+- Bug where ``pd.read_gbq`` throws ``ValueError`` when Bigquery returns zero rows (:issue:`10273`)

pandas/io/gbq.py

@@ -121,7 +121,7 @@ def get_service(self, credentials):
 
         try:
             from apiclient.discovery import build
-        
+
         except ImportError:
             raise ImportError('Could not import Google API Client.')
 
@@ -279,7 +279,7 @@ def _parse_data(schema, rows):
                                        field_type)
             page_array[row_num][col_num] = field_value
 
-    return DataFrame(page_array)
+    return DataFrame(page_array, columns=col_names)
 
 def _parse_entry(field_value, field_type):
     if field_value is None or field_value == 'null':
@@ -338,7 +338,10 @@ def read_gbq(query, project_id=None, index_col=None, col_order=None, reauth=Fals
         page = pages.pop()
         dataframe_list.append(_parse_data(schema, page))
 
-    final_df = concat(dataframe_list, ignore_index = True)
+    if len(dataframe_list) > 0:
+        final_df = concat(dataframe_list, ignore_index=True)
+    else:
+        final_df = _parse_data(schema, [])
 
     # Reindex the DataFrame on the provided column
     if index_col is not None:

pandas/io/tests/test_gbq.py

@@ -296,6 +296,13 @@ def test_download_dataset_larger_than_200k_rows(self):
         df = gbq.read_gbq("SELECT id FROM [publicdata:samples.wikipedia] GROUP EACH BY id ORDER BY id ASC LIMIT 200005", project_id=PROJECT_ID)
         self.assertEqual(len(df.drop_duplicates()), 200005)
 
+    def test_zero_rows(self):
+        # Bug fix for https://github.com/pydata/pandas/issues/10273
+        df = gbq.read_gbq("SELECT title, language  FROM [publicdata:samples.wikipedia] where timestamp=-9999999", project_id=PROJECT_ID)
+        expected_result = DataFrame(columns=['title', 'language'])
+        self.assert_frame_equal(df, expected_result)
+
+
 class TestToGBQIntegration(tm.TestCase):
     # This class requires bq.py to be installed for setup/teardown. 
     # It will also need to be preconfigured with a default dataset,