Cannot build optimal range on index ab for c = 10 and (a = 'xx' or (a = 'kk' and b = 1))

[xuyifangreeneyes]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(id int, a varchar(100), b int, c int, index idx_ab(a, b));
explain select * from t where c = 10 and (a = 'xx' or (a = 'kk' and b = 1));

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

mysql> explain select * from t where c = 10 and (a = 'xx' or (a = 'kk' and b = 1));
+-------------------------------+---------+-----------+-----------------------------+--------------------------------------------------------------------+
| id                            | estRows | task      | access object               | operator info                                                      |
+-------------------------------+---------+-----------+-----------------------------+--------------------------------------------------------------------+
| IndexLookUp_11                | 0.01    | root      |                             |                                                                    |
| ├─IndexRangeScan_8(Build)     | 10.10   | cop[tikv] | table:t, index:idx_ab(a, b) | range:["kk" 1,"kk" 1], ["xx","xx"], keep order:false, stats:pseudo |
| └─Selection_10(Probe)         | 0.01    | cop[tikv] |                             | eq(test.t.c, 10)                                                   |
|   └─TableRowIDScan_9          | 10.10   | cop[tikv] | table:t                     | keep order:false, stats:pseudo                                     |
+-------------------------------+---------+-----------+-----------------------------+--------------------------------------------------------------------+
4 rows in set (0.01 sec)

3. What did you see instead (Required)

mysql> explain select * from t where c = 10 and (a = 'xx' or (a = 'kk' and b = 1));
+----------------------------+---------+-----------+-----------------------------+------------------------------------------------------------------+
| id                         | estRows | task      | access object               | operator info                                                    |
+----------------------------+---------+-----------+-----------------------------+------------------------------------------------------------------+
| IndexLookUp_12             | 0.01    | root      |                             |                                                                  |
| ├─Selection_10(Build)      | 0.02    | cop[tikv] |                             | or(eq(test.t.a, "xx"), and(eq(test.t.a, "kk"), eq(test.t.b, 1))) |
| │ └─IndexRangeScan_8       | 20.00   | cop[tikv] | table:t, index:idx_ab(a, b) | range:["kk","kk"], ["xx","xx"], keep order:false, stats:pseudo   |
| └─Selection_11(Probe)      | 0.01    | cop[tikv] |                             | eq(test.t.c, 10)                                                 |
|   └─TableRowIDScan_9       | 0.02    | cop[tikv] | table:t                     | keep order:false, stats:pseudo                                   |
+----------------------------+---------+-----------+-----------------------------+------------------------------------------------------------------+
5 rows in set (0.01 sec)

4. What is your TiDB version? (Required)

master