fix: % replace in values_for_column (#28271)

superset/models/helpers.py

@@ -552,7 +552,6 @@ def modified(self) -> Markup:
 
 
 class QueryResult:  # pylint: disable=too-few-public-methods
-
     """Object returned by the query interface"""
 
     def __init__(  # pylint: disable=too-many-arguments
@@ -1377,10 +1376,14 @@ def values_for_column(
             qry = qry.where(self.get_fetch_values_predicate(template_processor=tp))
 
         with self.database.get_sqla_engine_with_context() as engine:
-            sql = qry.compile(engine, compile_kwargs={"literal_binds": True})
+            sql = str(qry.compile(engine, compile_kwargs={"literal_binds": True}))
             sql = self._apply_cte(sql, cte)
             sql = self.mutate_query_from_config(sql)
 
+            # pylint: disable=protected-access
+            if engine.dialect.identifier_preparer._double_percents:
+                sql = sql.replace("%%", "%")
+
             df = pd.read_sql_query(sql=sql, con=engine)
             # replace NaN with None to ensure it can be serialized to JSON
             df = df.replace({np.nan: None})