unexpected partition pruning result

[XuHuaiyu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

CREATE TABLE `t` (
  `a` int(11) DEFAULT NULL,
  `b` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
PARTITION BY RANGE COLUMNS(a) (
  PARTITION p0 VALUES LESS THAN (1),
  PARTITION p1 VALUES LESS THAN (10),
  PARTITION p2 VALUES LESS THAN (100)
);

desc select * from t where a = 11 and b = 1 or a = 12 and b = 1;

2. What did you expect to see?
   Partition p0 and p1 will not be accessed.

3. What did you see instead?
   All the partitions are accessed.

tidb> desc select * from t where a = 11 and b = 1 or a = 12 and b = 1;
+--------------------------+----------+-----------+------------------------------------------------------------------------------------+
| id                       | count    | task      | operator info                                                                      |
+--------------------------+----------+-----------+------------------------------------------------------------------------------------+
| Union_9                  | 24000.00 | root      |                                                                                    |
| ├─TableReader_12         | 8000.00  | root      | data:Selection_11                                                                  |
| │ └─Selection_11         | 8000.00  | cop[tikv] | or(and(eq(test.t.a, 11), eq(test.t.b, 1)), and(eq(test.t.a, 12), eq(test.t.b, 1))) |
| │   └─TableScan_10       | 10000.00 | cop[tikv] | table:t, partition:p0, range:[-inf,+inf], keep order:false, stats:pseudo           |
| ├─TableReader_15         | 8000.00  | root      | data:Selection_14                                                                  |
| │ └─Selection_14         | 8000.00  | cop[tikv] | or(and(eq(test.t.a, 11), eq(test.t.b, 1)), and(eq(test.t.a, 12), eq(test.t.b, 1))) |
| │   └─TableScan_13       | 10000.00 | cop[tikv] | table:t, partition:p1, range:[-inf,+inf], keep order:false, stats:pseudo           |
| └─TableReader_18         | 8000.00  | root      | data:Selection_17                                                                  |
|   └─Selection_17         | 8000.00  | cop[tikv] | or(and(eq(test.t.a, 11), eq(test.t.b, 1)), and(eq(test.t.a, 12), eq(test.t.b, 1))) |
|     └─TableScan_16       | 10000.00 | cop[tikv] | table:t, partition:p2, range:[-inf,+inf], keep order:false, stats:pseudo           |
+--------------------------+----------+-----------+------------------------------------------------------------------------------------+
10 rows in set (0.00 sec)

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

Release Version: v4.0.0-alpha-1373-g74bc00dfa
Git Commit Hash: 74bc00dfa953da06d8e5823d0acbf6bf1858a680
Git Branch: partition_prune
UTC Build Time: 2020-01-19 09:33:43
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false