expression: enable dayname/monthname function push down for tiflash

expression/expr_to_pb_test.go

@@ -1014,6 +1014,16 @@ func TestExprPushDownToFlash(t *testing.T) {
 	require.NoError(t, err)
 	exprs = append(exprs, function)
 
+	// DayName: supported
+	function, err = NewFunction(mock.NewContext(), ast.DayName, types.NewFieldType(mysql.TypeString), datetimeColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+
+	// MonthName: supported
+	function, err = NewFunction(mock.NewContext(), ast.MonthName, types.NewFieldType(mysql.TypeString), datetimeColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+
 	pushed, remained = PushDownExprs(sc, exprs, client, kv.TiFlash)
 	require.Len(t, pushed, len(exprs))
 	require.Len(t, remained, 0)

expression/expression.go

@@ -1052,7 +1052,7 @@ func scalarExprSupportedByFlash(function *ScalarFunction) bool {
 		ast.Plus, ast.Minus, ast.Div, ast.Mul, ast.Abs, ast.Mod,
 		ast.If, ast.Ifnull, ast.Case,
 		ast.Concat, ast.ConcatWS,
-		ast.Date, ast.Year, ast.Month, ast.Day, ast.Quarter,
+		ast.Date, ast.Year, ast.Month, ast.Day, ast.Quarter, ast.DayName, ast.MonthName,
 		ast.DateDiff, ast.TimestampDiff, ast.DateFormat, ast.FromUnixTime,
 
 		ast.Sqrt, ast.Log, ast.Log2, ast.Log10, ast.Ln, ast.Exp, ast.Pow, ast.Sign,