[get_df] Updating multi-statement logic (apache#5517)

superset/models/core.py

@@ -738,8 +738,12 @@ def needs_conversion(df_series):
 
         with closing(engine.raw_connection()) as conn:
             with closing(conn.cursor()) as cursor:
-                for sql in sqls:
+                for sql in sqls[:-1]:
                     self.db_engine_spec.execute(cursor, sql)
+                    cursor.fetchall()
+
+                self.db_engine_spec.execute(cursor, sqls[-1])
+
                 df = pd.DataFrame.from_records(
                     data=list(cursor.fetchall()),
                     columns=[col_desc[0] for col_desc in cursor.description],