Statistics cannot be generated correctly for a global index that has an expression index

[Defined2014]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

set tidb_enable_global_index=true;
drop table if exists t;
CREATE TABLE `t` (
  `a` int(11) DEFAULT NULL,
  `b` int(11) DEFAULT NULL,
  `c` int(11) DEFAULT NULL,
  UNIQUE KEY `idx` ((`c` + 1)),
  UNIQUE KEY `idx1` (`c`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
PARTITION BY HASH (`b`) PARTITIONS 2;
insert into t values (1,1,1),(2,2,2),(3,3,3),(4,4,4),(5,5,5);
analyze table t;
explain select c+1 from t where (c+1)>3;

2. What did you expect to see? (Required)

mysql> explain select c+1 from t where (c+1)>3;
+------------------------+---------+-----------+------------------------------+--------------------------------------------------------------------------+
| id                     | estRows | task      | access object                | operator info                                                            |
+------------------------+---------+-----------+------------------------------+--------------------------------------------------------------------------+
| IndexReader_6          | 3.00    | root      |                              | index:IndexRangeScan_5                                                   |
| └─IndexRangeScan_5     | 3.00    | cop[tikv] | table:t, index:idx(`c` + 1) | range:(3,+inf], keep order:false, stats:partial[_v$_idx_0:unInitialized] |
+------------------------+---------+-----------+------------------------------+--------------------------------------------------------------------------+
2 rows in set (0.01 sec)

3. What did you see instead (Required)

mysql> explain select c+1 from t where (c+1)>3;
+------------------------+---------+-----------+-----------------------------+--------------------------------------------------------------------------+
| id                     | estRows | task      | access object               | operator info                                                            |
+------------------------+---------+-----------+-----------------------------+--------------------------------------------------------------------------+
| IndexReader_7          | 2.08    | root      | partition:all               | index:IndexRangeScan_5                                                   |
| └─IndexRangeScan_5     | 2.08    | cop[tikv] | table:t, index:idx(`c` + 1) | range:(3,+inf], keep order:false, stats:partial[_v$_idx_0:unInitialized] |
+------------------------+---------+-----------+-----------------------------+--------------------------------------------------------------------------+
2 rows in set (0.01 sec)

The estRows are never changed, no matter what conditions are used to query, e.g. explain select c+1 from t where (c+1)>0;

4. What is your TiDB version? (Required)

[elsa0520]

Now, we don't have ability for global index

[Defined2014]

Now, we don't have ability for global index

Only affects expression index, it works well with normal global index.