BUG: to_sql convert index name to string (#15404) (#15423)

* Converted index name to string to fix issue #15404 - BUG: to_sql errors with numeric index name - needs conversion to string

* Additional int to string conversion added. Associated test cases added.

* PEP 8 compliance edits

* Removed extraneous brackets

Author: redbullpeter

pandas/io/sql.py

@@ -750,7 +750,8 @@ def _get_column_names_and_types(self, dtype_mapper):
             for i, idx_label in enumerate(self.index):
                 idx_type = dtype_mapper(
                     self.frame.index.get_level_values(i))
-                column_names_and_types.append((idx_label, idx_type, True))
+                column_names_and_types.append((text_type(idx_label),
+                                              idx_type, True))
 
         column_names_and_types += [
             (text_type(self.frame.columns[i]),
@@ -1220,7 +1221,7 @@ def _create_sql_schema(self, frame, table_name, keys=None, dtype=None):
 
 def _get_unicode_name(name):
     try:
-        uname = name.encode("utf-8", "strict").decode("utf-8")
+        uname = text_type(name).encode("utf-8", "strict").decode("utf-8")
     except UnicodeError:
         raise ValueError("Cannot convert identifier to UTF-8: '%s'" % name)
     return uname

pandas/tests/io/test_sql.py

@@ -709,6 +709,21 @@ def test_to_sql_index_label(self):
         self.assertEqual(frame.columns[0], 'other_label',
                          "Specified index_label not written to database")
 
+        # index name is integer
+        temp_frame.index.name = 0
+        sql.to_sql(temp_frame, 'test_index_label', self.conn,
+                   if_exists='replace')
+        frame = sql.read_sql_query('SELECT * FROM test_index_label', self.conn)
+        self.assertEqual(frame.columns[0], '0',
+                         "Integer index label not written to database")
+
+        temp_frame.index.name = None
+        sql.to_sql(temp_frame, 'test_index_label', self.conn,
+                   if_exists='replace', index_label=0)
+        frame = sql.read_sql_query('SELECT * FROM test_index_label', self.conn)
+        self.assertEqual(frame.columns[0], '0',
+                         "Integer index label not written to database")
+
     def test_to_sql_index_label_multiindex(self):
         temp_frame = DataFrame({'col1': range(4)},
                                index=MultiIndex.from_product(