executor: fix batch point get return wrong result for in(null)

executor/batch_point_get.go

@@ -143,6 +143,15 @@ func (e *BatchPointGetExec) Next(ctx context.Context, req *chunk.Chunk) error {
 	return nil
 }
 
+func datumsContainNull(vals []types.Datum) bool {
+	for _, val := range vals {
+		if val.IsNull() {
+			return true
+		}
+	}
+	return false
+}
+
 func (e *BatchPointGetExec) initialize(ctx context.Context) error {
 	var handleVals map[string][]byte
 	var indexKeys []kv.Key
@@ -153,6 +162,11 @@ func (e *BatchPointGetExec) initialize(ctx context.Context) error {
 		dedup := make(map[hack.MutableString]struct{})
 		keys := make([]kv.Key, 0, len(e.idxVals))
 		for _, idxVals := range e.idxVals {
+			// For all x, 'x IN (null)' evaluate to null, so the query get no result.
+			if datumsContainNull(idxVals) {
+				continue
+			}
+
 			physID := getPhysID(e.tblInfo, idxVals[e.partPos].GetInt64())
 			idxKey, err1 := EncodeUniqueIndexKey(e.ctx, e.tblInfo, e.idxInfo, idxVals, physID)
 			if err1 != nil && !kv.ErrNotExist.Equal(err1) {
@@ -175,6 +189,11 @@ func (e *BatchPointGetExec) initialize(ctx context.Context) error {
 		}
 		indexKeys = keys
 
+		// SELECT * FROM t WHERE x IN (null), in this case there is no key.
+		if len(keys) == 0 {
+			return nil
+		}
+
 		// Fetch all handles.
 		handleVals, err = batchGetter.BatchGet(ctx, keys)
 		if err != nil {

executor/batch_point_get_test.go

@@ -138,3 +138,15 @@ func (s *testBatchPointGetSuite) TestBatchPointGetCache(c *C) {
 	tk.MustQuery("SELECT id, token FROM test.customers WHERE id IN (28)")
 	tk.MustQuery("SELECT id, token FROM test.customers WHERE id IN (28, 29);").Check(testkit.Rows("28 07j", "29 03j"))
 }
+
+func (s *testBatchPointGetSuite) TestIssue18843(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t18843 ( id bigint(10) primary key, f varchar(191) default null, unique key `idx_f` (`f`))")
+	tk.MustExec("insert into t18843 values (1, '')")
+	tk.MustQuery("select * from t18843 where f in (null)").Check(testkit.Rows())
+
+	tk.MustExec("insert into t18843 values (2, null)")
+	tk.MustQuery("select * from t18843 where f in (null)").Check(testkit.Rows())
+	tk.MustQuery("select * from t18843 where f is null").Check(testkit.Rows("2 <nil>"))
+}