Index join inner range is not accurate for clustered index table

[xuyifangreeneyes]

Enhancement

mysql> create table t3(a int, b int, c int);
Query OK, 0 rows affected (0.03 sec)

mysql> create table t4(a int, b int, c int, primary key (a, b) clustered);
Query OK, 0 rows affected (0.03 sec)

mysql> explain select /*+ inl_join(t4) */ * from t3 join t4 on t3.b = t4.b where t4.a = 1;
+------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------------------------------------------------+
| id                           | estRows  | task      | access object | operator info                                                                                                   |
+------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------------------------------------------------+
| IndexJoin_14                 | 12.50    | root      |               | inner join, inner:TableReader_10, outer key:test.t3.b, inner key:test.t4.b, equal cond:eq(test.t3.b, test.t4.b) |
| ├─TableReader_20(Build)      | 9990.00  | root      |               | data:Selection_19                                                                                               |
| │ └─Selection_19             | 9990.00  | cop[tikv] |               | not(isnull(test.t3.b))                                                                                          |
| │   └─TableFullScan_18       | 10000.00 | cop[tikv] | table:t3      | keep order:false, stats:pseudo                                                                                  |
| └─TableReader_10(Probe)      | 0.00     | root      |               | data:Selection_9                                                                                                |
|   └─Selection_9              | 0.00     | cop[tikv] |               | eq(test.t4.a, 1)                                                                                                |
|     └─TableRangeScan_8       | 1.00     | cop[tikv] | table:t4      | range: decided by [test.t3.b], keep order:false, stats:pseudo                                                   |
+------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------------------------------------------------+
7 rows in set (0.02 sec)

range: decided by [test.t3.b] is not accurate. The more accurate range is range: decided by [eq(test.t4.b, test.t3.b) eq(test.t4.a, 1)].