agg_to_cop get panic on partitioned table

[XuHuaiyu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

set @@tidb_opt_agg_push_down=1;
CREATE TABLE `t1` (
  `a` int(11) DEFAULT NULL,
  `b` tinyint(4) NOT NULL,
  PRIMARY KEY (`b`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
PARTITION BY RANGE ( `b` ) (
  PARTITION `p0` VALUES LESS THAN (10),
  PARTITION `p1` VALUES LESS THAN (20),
  PARTITION `p2` VALUES LESS THAN (30),
  PARTITION `p3` VALUES LESS THAN (40),
  PARTITION `p4` VALUES LESS THAN (MAXVALUE)
);
insert into t1 values (0, 0), (1, 1), (1, 2), (1, 3), (2, 4), (2, 5), (2, 6), (3, 7), (3, 10), (3, 11), (12, 12), (12, 13), (14, 14), (14, 15), (20, 20), (20, 21), (20, 22), (23, 23), (23, 24), (23, 25), (31, 30), (31, 31), (31, 32), (33, 33), (33, 34), (33, 35), (36, 36), (80, 80), (90, 90), (100, 100);
select /*+ AGG_TO_COP() */ sum(a), sum(b) from t1 where a < 40 group by a;

2. What did you expect to see?

the query works fine

3. What did you see instead?

tidb>  select /*+ AGG_TO_COP() */ sum(a), sum(b) from t1 where a < 40 group by a;
ERROR 1105 (HY000): runtime error: index out of range [0] with length 0

4. What version of TiDB are you using? (tidb-server -V or run select tidb_version(); on TiDB)

tidb> select tidb_version();
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                        |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v4.0.0-beta.2-343-ge607157ef
Git Commit Hash: e607157efef0f76878d18a667b233061ce43545a
Git Branch: master
UTC Build Time: 2020-04-27 06:44:46
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

[lzmhhh123]

I can't reproduce in the newest master branch.

[XuHuaiyu]

@lzmhhh123
We need to set @@tidb_opt_agg_push_down=1;