TIDB_DECODE_KEY use partition id instead of table id

[olivia-chen-github]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

select TIDB_DECODE_KEY from information_schema.tikv_region_status

SELECT START_KEY, TIDB_DECODE_KEY(START_KEY) FROM information_schema.tikv_region_status WHERE table_name='stock' AND REGION_ID=49103157;
+--------------------------------------------------------------------------+----------------------------------------------+
| START_KEY                                                                | TIDB_DECODE_KEY(START_KEY)                   |
+--------------------------------------------------------------------------+----------------------------------------------+
| 748000000000035BFFA25F720380000000FF00001F3303800000FF0000011723000000FC | {"handle":"{7987, 71459}","table_id":220066} |
| 748000000000035BFFA25F720380000000FF00001F3303800000FF0000011723000000FC | {"handle":"{7987, 71459}","table_id":220066} |
| 748000000000035BFFA25F720380000000FF00001F3303800000FF0000011723000000FC | {"handle":"{7987, 71459}","table_id":220066} |
| 748000000000035BFFA25F720380000000FF00001F3303800000FF0000011723000000FC | {"handle":"{7987, 71459}","table_id":220066} |
+--------------------------------------------------------------------------+----------------------------------------------+

When we check the table, there's no table with id 220066
The real id for such table is 212078 instead

mysql> select tidb_table_id from information_schema.tables where table_name = 'stock';
+---------------+
| tidb_table_id |
+---------------+
|        212078 |
+---------------+
1 row in set (0.94 sec)

We found stock table is partitioned and the table id in the key is actually partition id

mysql> select * from partitions where TIDB_PARTITION_ID = 220066;
+---------------+-----------------+------------+----------------+-------------------+----------------------------+-------------------------------+------------------+---------------------+----------------------+-------------------------+-----------------------+------------+----------------+-------------+-----------------+--------------+-----------+---------------------+-------------+------------+----------+-------------------+-----------+-----------------+-------------------+----------------------------+
| TABLE_CATALOG | TABLE_SCHEMA    | TABLE_NAME | PARTITION_NAME | SUBPARTITION_NAME | PARTITION_ORDINAL_POSITION | SUBPARTITION_ORDINAL_POSITION | PARTITION_METHOD | SUBPARTITION_METHOD | PARTITION_EXPRESSION | SUBPARTITION_EXPRESSION | PARTITION_DESCRIPTION | TABLE_ROWS | AVG_ROW_LENGTH | DATA_LENGTH | MAX_DATA_LENGTH | INDEX_LENGTH | DATA_FREE | CREATE_TIME         | UPDATE_TIME | CHECK_TIME | CHECKSUM | PARTITION_COMMENT | NODEGROUP | TABLESPACE_NAME | TIDB_PARTITION_ID | TIDB_PLACEMENT_POLICY_NAME |
+---------------+-----------------+------------+----------------+-------------------+----------------------------+-------------------------------+------------------+---------------------+----------------------+-------------------------+-----------------------+------------+----------------+-------------+-----------------+--------------+-----------+---------------------+-------------+------------+----------+-------------------+-----------+-----------------+-------------------+----------------------------+
| def           | tpcc_load_test1 | stock      | p7987          | NULL              |                       7988 |                          NULL | HASH             | NULL                | `s_w_id`             | NULL                    |                       |          0 |              0 |           0 |               0 |            0 |         0 | 2022-11-12 02:28:31 | NULL        | NULL       |     NULL |                   | NULL      | NULL            |            220066 | NULL                       |
+---------------+-----------------+------------+----------------+-------------------+----------------------------+-------------------------------+------------------+---------------------+----------------------+-------------------------+-----------------------+------------+----------------+-------------+-----------------+--------------+-----------+---------------------+-------------+------------+----------+-------------------+-----------+-----------------+-------------------+----------------------------+
1 row in set (1.01 sec)

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

We expect TIDB_DECODE_KEY provides proper table id 212078 instead of 220066 which is the partition id of this table.

3. What did you see instead (Required)

Partition id 220066 is shown as table id in TIDB_DECODE_KEY
We found the current tidb_decode_key function is using partition id instead of table id.

tidb/planner/core/expression_rewriter.go

Line 2144 in e48f357

func decodeKeyFromString(ctx sessionctx.Context, s string) string {

4. What is your TiDB version? (Required)

v6.1.0