diff --git a/executor/aggregate.go b/executor/aggregate.go
index 8a6b83d089e58..85c7f64862b8e 100644
--- a/executor/aggregate.go
+++ b/executor/aggregate.go
@@ -572,11 +572,24 @@ func getGroupKey(ctx sessionctx.Context, input *chunk.Chunk, groupKey [][]byte,
 
 	for _, item := range groupByItems {
 		tp := item.GetType()
+
 		buf, err := expression.GetColumn(tp.EvalType(), numRows)
 		if err != nil {
 			return nil, err
 		}
 
+		// In strict sql mode like ‘STRICT_TRANS_TABLES’，can not insert an invalid enum value like 0.
+		// While in sql mode like '', can insert an invalid enum value like 0,
+		// then the enum value 0 will have the enum name '', which maybe conflict with user defined enum ''.
+		// Ref to issue #26885.
+		// This check is used to handle invalid enum name same with user defined enum name.
+		// Use enum value as groupKey instead of enum name.
+		if item.GetType().Tp == mysql.TypeEnum {
+			newTp := *tp
+			newTp.Flag |= mysql.EnumSetAsIntFlag
+			tp = &newTp
+		}
+
 		if err := expression.EvalExpr(ctx, item, tp.EvalType(), input, buf); err != nil {
 			expression.PutColumn(buf)
 			return nil, err
@@ -587,6 +600,7 @@ func getGroupKey(ctx sessionctx.Context, input *chunk.Chunk, groupKey [][]byte,
 			newTp.Flen = 0
 			tp = &newTp
 		}
+
 		groupKey, err = codec.HashGroupKey(ctx.GetSessionVars().StmtCtx, input.NumRows(), buf, groupKey, tp)
 		if err != nil {
 			expression.PutColumn(buf)
diff --git a/executor/aggregate_test.go b/executor/aggregate_test.go
index 976775ce5dc4c..a4e5c9cee0ac8 100644
--- a/executor/aggregate_test.go
+++ b/executor/aggregate_test.go
@@ -1597,3 +1597,36 @@ func TestRandomPanicAggConsume(t *testing.T) {
 		require.EqualError(t, err, "failpoint panic: ERROR 1105 (HY000): Out Of Memory Quota![conn_id=1]")
 	}
 }
+
+func TestIssue26885(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec(`use test`)
+	tk.MustExec(`SET sql_mode = 'NO_ENGINE_SUBSTITUTION';`)
+	tk.MustExec(`DROP TABLE IF EXISTS t1;`)
+
+	tk.MustExec("CREATE TABLE t1 (c1 ENUM('a', '', 'b'));")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES ('b');")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES ('');")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES ('a');")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES ('');")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES (0);")
+	tk.MustQuery("select * from t1").Check(testkit.Rows("b", "", "a", "", ""))
+	tk.MustQuery("select c1 + 0 from t1").Check(testkit.Rows("3", "2", "1", "2", "0"))
+	tk.MustQuery("SELECT c1 + 0, COUNT(c1) FROM t1 GROUP BY c1 order by c1;").Check(testkit.Rows("0 1", "1 1", "2 2", "3 1"))
+
+	tk.MustExec("alter table t1 add index idx(c1); ")
+	tk.MustQuery("select c1 + 0 from t1").Check(testkit.Rows("3", "2", "1", "2", "0"))
+	tk.MustQuery("SELECT c1 + 0, COUNT(c1) FROM t1 GROUP BY c1 order by c1;").Check(testkit.Rows("0 1", "1 1", "2 2", "3 1"))
+
+	tk.MustExec(`DROP TABLE IF EXISTS t1;`)
+	tk.MustExec("CREATE TABLE t1 (c1 ENUM('a', 'b', 'c'));")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES ('b');")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES ('a');")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES ('b');")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES ('c');")
+	tk.MustExec("INSERT INTO t1 (c1) VALUES (0);")
+	tk.MustQuery("select * from t1").Check(testkit.Rows("b", "a", "b", "c", ""))
+	tk.MustQuery("SELECT c1 + 0, COUNT(c1) FROM t1 GROUP BY c1 order by c1;").Check(testkit.Rows("0 1", "1 1", "2 2", "3 1"))
+}