expression: fix wrong result when convert float to unsigned (pingcap#53590)

close pingcap#41736

Author: guo-shaoge

pkg/expression/builtin_compare.go

@@ -1428,7 +1428,10 @@ func RefineComparedConstant(ctx BuildContext, targetFieldType types.FieldType, c
 		targetFieldType = *types.NewFieldType(mysql.TypeLonglong)
 	}
 	var intDatum types.Datum
-	intDatum, err = dt.ConvertTo(evalCtx.TypeCtx(), &targetFieldType)
+	// Disable AllowNegativeToUnsigned to make sure return 0 when underflow happens.
+	oriTypeCtx := evalCtx.TypeCtx()
+	newTypeCtx := oriTypeCtx.WithFlags(oriTypeCtx.Flags().WithAllowNegativeToUnsigned(false))
+	intDatum, err = dt.ConvertTo(newTypeCtx, &targetFieldType)
 	if err != nil {
 		if terror.ErrorEqual(err, types.ErrOverflow) {
 			return &Constant{

tests/integrationtest/r/expression/cast.result

@@ -118,3 +118,33 @@ select null as a union all select 'a' as a;
 a
 NULL
 a
+drop table if exists t0;
+create table t0(c0 tinyint(1) unsigned not null );
+insert into t0 values (1);
+select * from t0 where case 0 when t0.c0 > -1.194192591e9 then null else 1 end;
+c0
+1
+select t0.c0 > -1.194192591e9 from t0;
+t0.c0 > -1.194192591e9
+1
+select t0.c0 < -1.194192591e9 from t0;
+t0.c0 < -1.194192591e9
+0
+select -1.194192591e9 > t0.c0 from t0;
+-1.194192591e9 > t0.c0
+0
+select -1.194192591e9 < t0.c0 from t0;
+-1.194192591e9 < t0.c0
+1
+select t0.c0 > 1.194192591e9 from t0;
+t0.c0 > 1.194192591e9
+0
+select t0.c0 < 1.194192591e9 from t0;
+t0.c0 < 1.194192591e9
+1
+select 1.194192591e9 > t0.c0 from t0;
+1.194192591e9 > t0.c0
+1
+select 1.194192591e9 < t0.c0 from t0;
+1.194192591e9 < t0.c0
+0

tests/integrationtest/t/expression/cast.test

@@ -73,3 +73,17 @@ select cast(cast('14:15' as time) as year) = YEAR(CURDATE());
 explain select null as a union all select 'a' as a;
 --sorted_result
 select null as a union all select 'a' as a;
+
+# TestNegFloatConvertToUnsigned
+drop table if exists t0;
+create table t0(c0 tinyint(1) unsigned not null );
+insert into t0 values (1);
+select * from t0 where case 0 when t0.c0 > -1.194192591e9 then null else 1 end;
+select t0.c0 > -1.194192591e9 from t0;
+select t0.c0 < -1.194192591e9 from t0;
+select -1.194192591e9 > t0.c0 from t0;
+select -1.194192591e9 < t0.c0 from t0;
+select t0.c0 > 1.194192591e9 from t0;
+select t0.c0 < 1.194192591e9 from t0;
+select 1.194192591e9 > t0.c0 from t0;
+select 1.194192591e9 < t0.c0 from t0;