expr: forbid push round with frac down (#32666)

close pingcap/tidb#32557

expression/expression.go

@@ -1008,8 +1008,9 @@ func scalarExprSupportedByTiKV(sf *ScalarFunction) bool {
 		return true
 	case ast.Round:
 		switch sf.Function.PbCode() {
-		case tipb.ScalarFuncSig_RoundReal, tipb.ScalarFuncSig_RoundInt, tipb.ScalarFuncSig_RoundDec,
-			tipb.ScalarFuncSig_RoundWithFracReal, tipb.ScalarFuncSig_RoundWithFracInt, tipb.ScalarFuncSig_RoundWithFracDec:
+		case tipb.ScalarFuncSig_RoundReal, tipb.ScalarFuncSig_RoundInt, tipb.ScalarFuncSig_RoundDec:
+			// We don't push round with frac due to mysql's round with frac has its special behavior:
+			// https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_round
 			return true
 		}
 	case ast.Rand:

planner/core/integration_test.go

@@ -2829,10 +2829,6 @@ func TestScalarFunctionPushDown(t *testing.T) {
 	tk.MustQuery("explain analyze select /*+read_from_storage(tikv[t])*/ * from t where round(b)").
 		CheckAt([]int{0, 3, 6}, rows)
 
-	rows[1][2] = "round(test.t.b, 2)"
-	tk.MustQuery("explain analyze select /*+read_from_storage(tikv[t])*/ * from t where round(b,2)").
-		CheckAt([]int{0, 3, 6}, rows)
-
 	rows[1][2] = "date(test.t.d)"
 	tk.MustQuery("explain analyze select /*+read_from_storage(tikv[t])*/ * from t where date(d)").
 		CheckAt([]int{0, 3, 6}, rows)