[sql lab] fix csv export where % in query (#2711)

* [sql lab] fix csv export where  in query

* Prgoress

superset/models/core.py

@@ -575,16 +575,19 @@ def get_quoter(self):
     def get_df(self, sql, schema):
         sql = sql.strip().strip(';')
         eng = self.get_sqla_engine(schema=schema)
-        cur = eng.execute(sql, schema=schema)
-        cols = [col[0] for col in cur.cursor.description]
-        df = pd.DataFrame(cur.fetchall(), columns=cols)
+
+        conn = eng.raw_connection()
+        cur = conn.cursor()
+        cur.execute(sql, **self.db_engine_spec.cursor_execute_kwargs)
+
+        cols = [col[0] for col in cur.description]
+        df = pd.DataFrame(list(cur.fetchall()), columns=cols)
 
         def needs_conversion(df_series):
             if df_series.empty:
                 return False
-            for df_type in [list, dict]:
-                if isinstance(df_series[0], df_type):
-                    return True
+            if isinstance(df_series[0], (list, dict)):
+                return True
             return False
 
         for k, v in df.dtypes.iteritems():