From 106d171248b90df54f407047269efd790e2a4488 Mon Sep 17 00:00:00 2001
From: yanweiqi <592838129@qq.com>
Date: Fri, 22 Jul 2022 14:05:09 +0800
Subject: [PATCH] cherry pick #36208 to release-5.1

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
---
 executor/aggregate.go      | 14 ++++++++++++++
 executor/aggregate_test.go | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/executor/aggregate.go b/executor/aggregate.go
index 7cd0165a17691..c180d6d91fb51 100644
--- a/executor/aggregate.go
+++ b/executor/aggregate.go
@@ -517,11 +517,24 @@ 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().GetType() == mysql.TypeEnum {
+			newTp := *tp
+			newTp.AddFlag(mysql.EnumSetAsIntFlag)
+			tp = &newTp
+		}
+
 		if err := expression.EvalExpr(ctx, item, tp.EvalType(), input, buf); err != nil {
 			expression.PutColumn(buf)
 			return nil, err
@@ -532,6 +545,7 @@ 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 3e84256d79138..153519688936d 100644
--- a/executor/aggregate_test.go
+++ b/executor/aggregate_test.go
@@ -1490,3 +1490,36 @@ func (s *testSuiteAgg) TestIssue23314(c *C) {
 	res := tk.MustQuery("select col1 from t1 group by col1")
 	res.Check(testkit.Rows("16:40:20.01"))
 }
+
+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"))
+}