planner: wrong slice length check for index merge's order prop push down (#43465)

close pingcap/tidb#43178

planner/core/issuetest/BUILD.bazel

@@ -0,0 +1,10 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_test")
+
+go_test(
+    name = "issuetest_test",
+    timeout = "short",
+    srcs = ["planner_issue_test.go"],
+    flaky = True,
+    race = "on",
+    deps = ["//testkit"],
+)

planner/core/issuetest/planner_issue_test.go

@@ -0,0 +1,42 @@
+// Copyright 2022 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package issuetest
+
+import (
+	"testing"
+
+	"github.com/pingcap/tidb/testkit"
+)
+
+// It's a case for index merge's order prop push down.
+func TestIssue43178(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec(`CREATE TABLE aa311c3c (
+		57fd8d09 year(4) DEFAULT '1913',
+		afbdd7c3 char(220) DEFAULT 'gakkl6occ0yd2jmhi2qxog8szibtcqwxyxmga3hp4ktszjplmg3rjvu8v6lgn9q6hva2lekhw6napjejbut6svsr8q2j8w8rc551e5vq',
+		43b06e99 date NOT NULL DEFAULT '3403-10-08',
+		b80b3746 tinyint(4) NOT NULL DEFAULT '34',
+		6302d8ac timestamp DEFAULT '2004-04-01 18:21:18',
+		PRIMARY KEY (43b06e99,b80b3746) /*T![clustered_index] CLUSTERED */,
+		KEY 3080c821 (57fd8d09,43b06e99,b80b3746),
+		KEY a9af33a4 (57fd8d09,b80b3746,43b06e99),
+		KEY 464b386e (b80b3746),
+		KEY 19dc3c2d (57fd8d09)
+	      ) ENGINE=InnoDB DEFAULT CHARSET=ascii COLLATE=ascii_bin COMMENT='320f8401'`)
+	// Should not panic
+	tk.MustExec("explain select  /*+ use_index_merge( `aa311c3c` ) */   `aa311c3c`.`43b06e99` as r0 , `aa311c3c`.`6302d8ac` as r1 from `aa311c3c` where IsNull( `aa311c3c`.`b80b3746` ) or not( `aa311c3c`.`57fd8d09` >= '2008' )   order by r0,r1 limit 95")
+}

planner/core/task.go

@@ -1248,7 +1248,7 @@ func (p *PhysicalTopN) checkOrderPropForSubIndexScan(idxCols []*expression.Colum
 				idxPos++
 				break
 			}
-			if len(constColsByCond) == 0 || idxPos > len(constColsByCond) || !constColsByCond[idxPos] {
+			if idxPos >= len(constColsByCond) || !constColsByCond[idxPos] {
 				found = false
 				break
 			}