From aaa770ac718438225ce7602548bdfa534a0ee45e Mon Sep 17 00:00:00 2001
From: ti-srebot <66930949+ti-srebot@users.noreply.github.com>
Date: Tue, 11 May 2021 23:37:39 +0800
Subject: [PATCH] statistics: fix a bug which causes panic when using the
 clustered index and the new collation (#21379) (#21408)

---
 expression/integration_test.go | 18 ++++++++++++++++++
 statistics/histogram.go        | 12 ++----------
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/expression/integration_test.go b/expression/integration_test.go
index ae7f4eddea2de..0f145e41d2765 100755
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -7748,6 +7748,24 @@ func (s *testIntegrationSerialSuite) TestCollationIndexJoin(c *C) {
 	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1815 Optimizer Hint /*+ INL_MERGE_JOIN(t2) */ is inapplicable"))
 }
 
+func (s *testIntegrationSerialSuite) TestIssue20876(c *C) {
+	collate.SetNewCollationEnabledForTest(true)
+	defer collate.SetNewCollationEnabledForTest(false)
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t;")
+	tk.MustExec("CREATE TABLE `t` (" +
+		"  `a` char(10) COLLATE utf8mb4_unicode_ci NOT NULL," +
+		"  `b` char(20) COLLATE utf8mb4_general_ci NOT NULL," +
+		"  `c` int(11) NOT NULL," +
+		"  PRIMARY KEY (`a`,`b`,`c`)," +
+		"  KEY `idx` (`a`)" +
+		")")
+	tk.MustExec("insert into t values ('#', 'C', 10), ('$', 'c', 20), ('$', 'c', 30), ('a', 'a', 10), ('A', 'A', 30)")
+	tk.MustExec("analyze table t")
+	tk.MustQuery("select * from t where a='#';").Check(testkit.Rows("# C 10"))
+}
+
 func (s *testIntegrationSuite) TestIssue19892(c *C) {
 	defer s.cleanEnv(c)
 	tk := testkit.NewTestKit(c, s.store)
diff --git a/statistics/histogram.go b/statistics/histogram.go
index 76cbfe1732d07..af3861a2184a3 100644
--- a/statistics/histogram.go
+++ b/statistics/histogram.go
@@ -793,18 +793,10 @@ func (c *Column) GetColumnRowCount(sc *stmtctx.StatementContext, ranges []*range
 		highVal := *rg.HighVal[0].Clone()
 		lowVal := *rg.LowVal[0].Clone()
 		if highVal.Kind() == types.KindString {
-			highVal.SetBytesAsString(collate.GetCollator(
-				highVal.Collation()).Key(highVal.GetString()),
-				highVal.Collation(),
-				uint32(highVal.Length()),
-			)
+			highVal.SetBytes(collate.GetCollator(highVal.Collation()).Key(highVal.GetString()))
 		}
 		if lowVal.Kind() == types.KindString {
-			lowVal.SetBytesAsString(collate.GetCollator(
-				lowVal.Collation()).Key(lowVal.GetString()),
-				lowVal.Collation(),
-				uint32(lowVal.Length()),
-			)
+			lowVal.SetBytes(collate.GetCollator(lowVal.Collation()).Key(lowVal.GetString()))
 		}
 		cmp, err := lowVal.CompareDatum(sc, &highVal)
 		if err != nil {