*: fix bug that UnionScan can't keep order caused wrong result (#33218)…

… (#37805)

close #33175

executor/table_reader.go

@@ -181,6 +181,18 @@ func (e *TableReaderExecutor) Open(ctx context.Context) error {
 	// Calculate the kv ranges here, UnionScan rely on this kv ranges.
 	// cached table and temporary table are similar
 	if e.table.Meta() != nil && e.table.Meta().TempTableType != model.TempTableNone {
+		if e.desc && len(secondPartRanges) != 0 {
+			// TiKV support reverse scan and the `resultHandler` process the range order.
+			// While in UnionScan, it doesn't use reverse scan and reverse the final result rows manually.
+			// So things are differ, we need to reverse the kv range here.
+			// TODO: If we refactor UnionScan to use reverse scan, update the code here.
+			// [9734095886065816708 9734095886065816709] | [1 3] [65535 9734095886065816707] => before the following change
+			// [1 3] [65535 9734095886065816707] | [9734095886065816708 9734095886065816709] => ranges part reverse here
+			// [1 3  65535 9734095886065816707 9734095886065816708 9734095886065816709] => scan (normal order) in UnionScan
+			// [9734095886065816709 9734095886065816708 9734095886065816707 65535 3  1] => rows reverse in UnionScan
+			firstPartRanges, secondPartRanges = secondPartRanges, firstPartRanges
+		}
+
 		kvReq, err := e.buildKVReq(ctx, firstPartRanges)
 		if err != nil {
 			return err

planner/core/handle_cols.go

@@ -239,15 +239,9 @@ func (ib *IntHandleCols) NumCols() int {
 
 // Compare implements the kv.HandleCols interface.
 func (ib *IntHandleCols) Compare(a, b []types.Datum, ctors []collate.Collator) (int, error) {
-	aInt := a[ib.col.Index].GetInt64()
-	bInt := b[ib.col.Index].GetInt64()
-	if aInt == bInt {
-		return 0, nil
-	}
-	if aInt < bInt {
-		return -1, nil
-	}
-	return 1, nil
+	aVal := &a[ib.col.Index]
+	bVal := &b[ib.col.Index]
+	return aVal.Compare(nil, bVal, ctors[ib.col.Index])
 }
 
 // GetFieldsTypes implements the kv.HandleCols interface.

planner/core/integration_test.go

@@ -5347,3 +5347,59 @@ func (s *testIntegrationSuite) TestDNFCondSelectivityWithConst(c *C) {
 		"[  └─TableFullScan_5 129.00 cop[tikv] table:t1 keep order:false"))
 	testKit.MustExec("drop table if exists t1")
 }
+
+func (s *testIntegrationSuite) TestIssue33175(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t (id bigint(45) unsigned not null, c varchar(20), primary key(id));")
+	tk.MustExec("insert into t values (9734095886065816707, 'a'), (10353107668348738101, 'b'), (0, 'c');")
+	tk.MustExec("begin")
+	tk.MustExec("insert into t values (33, 'd');")
+	tk.MustQuery("select max(id) from t;").Check(testkit.Rows("10353107668348738101"))
+	tk.MustExec("rollback")
+
+	// With subquery, like the original issue case.
+	tk.MustQuery("select * from t where id > (select  max(id) from t where t.id > 0);").Check(testkit.Rows())
+
+	// Test order by desc / asc.
+	tk.MustQuery("select id from t order by id desc;").Check(testkit.Rows(
+		"10353107668348738101",
+		"9734095886065816707",
+		"0"))
+
+	tk.MustQuery("select id from t order by id asc;").Check(testkit.Rows(
+		"0",
+		"9734095886065816707",
+		"10353107668348738101"))
+
+	tk.MustExec("drop table t")
+
+	// Cover more code that use union scan
+	// TableReader/IndexReader/IndexLookup
+	for idx, q := range []string{
+		"create temporary table t (id bigint unsigned, c int default null, index(id))",
+		"create temporary table t (id bigint unsigned primary key)",
+	} {
+		tk.MustExec(q)
+		tk.MustExec("insert into t(id) values (1), (3), (9734095886065816707), (9734095886065816708)")
+		tk.MustQuery("select min(id) from t").Check(testkit.Rows("1"))
+		tk.MustQuery("select max(id) from t").Check(testkit.Rows("9734095886065816708"))
+		tk.MustQuery("select id from t order by id asc").Check(testkit.Rows(
+			"1", "3", "9734095886065816707", "9734095886065816708"))
+		tk.MustQuery("select id from t order by id desc").Check(testkit.Rows(
+			"9734095886065816708", "9734095886065816707", "3", "1"))
+		if idx == 0 {
+			tk.MustQuery("select * from t order by id asc").Check(testkit.Rows(
+				"1 <nil>",
+				"3 <nil>",
+				"9734095886065816707 <nil>",
+				"9734095886065816708 <nil>"))
+			tk.MustQuery("select * from t order by id desc").Check(testkit.Rows(
+				"9734095886065816708 <nil>",
+				"9734095886065816707 <nil>",
+				"3 <nil>",
+				"1 <nil>"))
+		}
+		tk.MustExec("drop table t")
+	}
+}