adding @wasade suggestion

Author: antgonza

qiita_db/metadata_template/base_metadata_template.py

@@ -1182,10 +1182,9 @@ def _common_to_dataframe_steps(self, samples=None):
                 sql += ' AND sample_id IN %s'
                 qdb.sql_connection.TRN.add(sql, [tuple(samples)])
 
-            df = pd.DataFrame(qdb.sql_connection.TRN.execute_fetchindex())
-            df = pd.concat([df.drop(1, axis=1),
-                            pd.DataFrame(df[1].tolist(), dtype='str')], axis=1)
-            df.set_index(0, inplace=True)
+            data = qdb.sql_connection.TRN.execute_fetchindex()
+            df = pd.DataFrame([d for _, d in data], index=[i for i, _ in data],
+                              dtype=str)
             df.index.name = 'sample_id'
             df.where((pd.notnull(df)), None)
             id_column_name = 'qiita_%sid' % (self._table_prefix)