executor, planner: fix collation for hash join building

executor/builder.go

@@ -2360,6 +2360,12 @@ func (b *executorBuilder) buildIndexLookUpJoin(v *plannercore.PhysicalIndexJoin)
 		}
 	}
 
+	// Use the probe table's collation.
+	for i, col := range v.OuterHashKeys {
+		outerTypes[col.Index] = outerTypes[col.Index].Clone()
+		outerTypes[col.Index].Collate = innerTypes[v.InnerHashKeys[i].Index].Collate
+	}
+
 	var (
 		outerFilter           []expression.Expression
 		leftTypes, rightTypes []*types.FieldType

expression/integration_test.go

@@ -8289,6 +8289,32 @@ 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) TestCollationMergeJoin(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` (" +
+		"  `col_10` blob DEFAULT NULL," +
+		"  `col_11` decimal(17,5) NOT NULL," +
+		"  `col_13` varchar(381) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT 'Yr'," +
+		"  PRIMARY KEY (`col_13`,`col_11`) CLUSTERED," +
+		"  KEY `idx_4` (`col_10`(3))" +
+		") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin")
+	tk.MustExec("insert into t values ('a', 12523, 'A');")
+	tk.MustExec("insert into t values ('A', 2, 'a');")
+	tk.MustExec("insert into t values ('a', 23, 'A');")
+	tk.MustExec("insert into t values ('a', 23, 'h2');")
+	tk.MustExec("insert into t values ('a', 23, 'h3');")
+	tk.MustExec("insert into t values ('a', 23, 'h4');")
+	tk.MustExec("insert into t values ('a', 23, 'h5');")
+	tk.MustExec("insert into t values ('a', 23, 'h6');")
+	tk.MustExec("insert into t values ('a', 23, 'h7');")
+	tk.MustQuery("select /*+ MERGE_JOIN(t) */ t.* from t where col_13 in ( select col_10 from t where t.col_13 in ( 'a', 'b' ) ) order by col_10 ;").Check(
+		testkit.Rows("\x41 2.00000 a", "\x61 23.00000 A", "\x61 12523.00000 A"))
+}
+
 func (s *testIntegrationSuite) TestIssue19892(c *C) {
 	defer s.cleanEnv(c)
 	tk := testkit.NewTestKit(c, s.store)
@@ -8980,6 +9006,7 @@ func (s *testIntegrationSerialSuite) TestCollationPrefixClusteredIndex(c *C) {
 	collate.SetNewCollationEnabledForTest(true)
 	defer collate.SetNewCollationEnabledForTest(false)
 
+	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t (k char(20), v int, primary key (k(4)) clustered, key (k)) collate utf8mb4_general_ci;")
 	tk.MustExec("insert into t values('01233', 1);")
 	tk.MustExec("create index idx on t(k(2))")

planner/core/exhaust_physical_plans.go

@@ -479,16 +479,7 @@ func (p *LogicalJoin) constructIndexJoin(
 		IsNullEQ:        newIsNullEQ,
 		DefaultValues:   p.DefaultValues,
 	}
-	// Correct the collation used by hash.
-	for i := range outerHashKeys {
-		// Make compiler happy.
-		if len(innerHashKeys) == 0 {
-			return nil
-		}
-		chs, coll := expression.DeriveCollationFromExprs(nil, outerHashKeys[i], innerHashKeys[i])
-		outerHashKeys[i].GetType().Charset, outerHashKeys[i].GetType().Collate = chs, coll
-		innerHashKeys[i].GetType().Charset, innerHashKeys[i].GetType().Collate = chs, coll
-	}
+
 	join := PhysicalIndexJoin{
 		basePhysicalJoin: baseJoin,
 		innerTask:        innerTask,