cherry pick pingcap#33523 to release-6.0

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

expression/builtin_encryption_vec.go

@@ -567,6 +567,7 @@ func (b *builtinCompressSig) vecEvalString(input *chunk.Chunk, result *chunk.Col
 		// According to doc: Empty strings are stored as empty strings.
 		if len(strBytes) == 0 {
 			result.AppendString("")
+			continue
 		}
 
 		compressed, err := deflate(strBytes)

expression/integration_test.go

@@ -7078,3 +7078,16 @@ func TestIssue32488(t *testing.T) {
 	tk.MustQuery("select binary upper(a), lower(a) from t order by upper(a);").Check([][]interface{}{{"İ i"}, {"Ʞ ʞ"}})
 	tk.MustQuery("select distinct upper(a), lower(a) from t order by upper(a);").Check([][]interface{}{{"İ i"}, {"Ʞ ʞ"}})
 }
+
+func TestIssue33397(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t(a varchar(32)) DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;")
+	tk.MustExec("insert into t values(''), ('');")
+	tk.MustExec("set @@tidb_enable_vectorized_expression = true;")
+	result := tk.MustQuery("select compress(a) from t").Rows()
+	require.Equal(t, [][]interface{}{{""}, {""}}, result)
+}