Fixed incorrect datatype conversion on multi-indexes

doc/source/v0.15.0.txt

@@ -446,6 +446,7 @@ There are no experimental changes in 0.15.0
 
 Bug Fixes
 ~~~~~~~~~
+- Bug in multiindexes dtypes getting mixed up when DataFrame is saved to SQL table (:issue:`8021`)
 - Bug in Series 0-division with a float and integer operand dtypes  (:issue:`7785`)
 - Bug in ``Series.astype("unicode")`` not calling ``unicode`` on the values correctly (:issue:`7758`)
 - Bug in ``DataFrame.as_matrix()`` with mixed ``datetime64[ns]`` and ``timedelta64[ns]`` dtypes (:issue:`7778`)

pandas/io/sql.py

@@ -664,20 +664,28 @@ def _index_name(self, index, index_label):
         else:
             return None
 
+    def _get_column_names_and_types(self, dtype_mapper):
+        column_names_and_types = []
+        if self.index is not None:
+            for i, idx_label in enumerate(self.index):
+                idx_type = dtype_mapper(
+                    self.frame.index.get_level_values(i).dtype)
+                column_names_and_types.append((idx_label, idx_type))
+
+        column_names_and_types += zip(
+            list(map(str, self.frame.columns)),
+            map(dtype_mapper, self.frame.dtypes)
+            )
+        return column_names_and_types
+
     def _create_table_statement(self):
         from sqlalchemy import Table, Column
 
-        columns = list(map(str, self.frame.columns))
-        column_types = map(self._sqlalchemy_type, self.frame.dtypes)
+        column_names_and_types = \
+            self._get_column_names_and_types(self._sqlalchemy_type)
 
         columns = [Column(name, typ)
-                   for name, typ in zip(columns, column_types)]
-
-        if self.index is not None:
-            for i, idx_label in enumerate(self.index[::-1]):
-                idx_type = self._sqlalchemy_type(
-                    self.frame.index.get_level_values(i))
-                columns.insert(0, Column(idx_label, idx_type, index=True))
+                   for name, typ in column_names_and_types]
 
         return Table(self.name, self.pd_sql.meta, *columns)
 
@@ -957,16 +965,13 @@ def insert(self):
     def _create_table_statement(self):
         "Return a CREATE TABLE statement to suit the contents of a DataFrame."
 
-        columns = list(map(str, self.frame.columns))
+        column_names_and_types = \
+            self._get_column_names_and_types(self._sql_type_name)
+
         pat = re.compile('\s+')
-        if any(map(pat.search, columns)):
+        column_names = [col_name for col_name, _ in column_names_and_types]
+        if any(map(pat.search, column_names)):
             warnings.warn(_SAFE_NAMES_WARNING)
-        column_types = [self._sql_type_name(typ) for typ in self.frame.dtypes]
-
-        if self.index is not None:
-            for i, idx_label in enumerate(self.index[::-1]):
-                columns.insert(0, idx_label)
-                column_types.insert(0, self._sql_type_name(self.frame.index.get_level_values(i).dtype))
 
         flv = self.pd_sql.flavor
 
@@ -976,7 +981,7 @@ def _create_table_statement(self):
         col_template = br_l + '%s' + br_r + ' %s'
 
         columns = ',\n  '.join(col_template %
-                               x for x in zip(columns, column_types))
+                               x for x in column_names_and_types)
         template = """CREATE TABLE %(name)s (
                       %(columns)s
                       )"""

pandas/io/tests/test_sql.py

@@ -581,6 +581,15 @@ def test_to_sql_index_label_multiindex(self):
                           'test_index_label', self.conn, if_exists='replace',
                           index_label='C')
 
+    def test_multiindex_roundtrip(self):
+        df = DataFrame.from_records([(1,2.1,'line1'), (2,1.5,'line2')], 
+                                    columns=['A','B','C'], index=['A','B'])
+
+        df.to_sql('test_multiindex_roundtrip', self.conn)
+        result = sql.read_sql_query('SELECT * FROM test_multiindex_roundtrip', 
+                                    self.conn, index_col=['A','B'])
+        tm.assert_frame_equal(df, result, check_index_type=True)        
+
     def test_integer_col_names(self):
         df = DataFrame([[1, 2], [3, 4]], columns=[0, 1])
         sql.to_sql(df, "test_frame_integer_col_names", self.conn,
@@ -641,9 +650,7 @@ def test_read_sql_delegate(self):
             "SELECT * FROM iris", self.conn)
         iris_frame2 = sql.read_sql(
             "SELECT * FROM iris", self.conn)
-        tm.assert_frame_equal(iris_frame1, iris_frame2,
-                              "read_sql and read_sql_query have not the same"
-                              " result with a query")
+        tm.assert_frame_equal(iris_frame1, iris_frame2)
 
         iris_frame1 = sql.read_sql_table('iris', self.conn)
         iris_frame2 = sql.read_sql('iris', self.conn)
@@ -697,9 +704,7 @@ def test_sql_open_close(self):
     def test_read_sql_delegate(self):
         iris_frame1 = sql.read_sql_query("SELECT * FROM iris", self.conn)
         iris_frame2 = sql.read_sql("SELECT * FROM iris", self.conn)
-        tm.assert_frame_equal(iris_frame1, iris_frame2,
-                              "read_sql and read_sql_query have not the same"
-                              " result with a query")
+        tm.assert_frame_equal(iris_frame1, iris_frame2)
 
         self.assertRaises(sql.DatabaseError, sql.read_sql, 'iris', self.conn)