ddl: support showing label rule through information schema table

[rleungx]

What problem does this PR solve?

Closes #26694. It can be reviewed after #26630 is merged.

What is changed and how it works?

This PR is going to provide a way to show the label rules through SQL.

mysql> create table t1 (c int);
Query OK, 0 rows affected (0.08 sec)

mysql> alter table t1 attributes="attr";
Query OK, 0 rows affected (0.07 sec)

mysql> select * from information_schema.region_label;
+----------------+-----------+--------------+--------------------------------------+--------------------------------------+
| RULE_ID        | RULE_TYPE | REGION_LABEL | START_KEY                            | END_KEY                              |
+----------------+-----------+--------------+--------------------------------------+--------------------------------------+
| schema/test/t1 | key-range | "attr"       | 7480000000000000ff355f720000000000fa | 7480000000000000ff365f720000000000fa |
+----------------+-----------+--------------+--------------------------------------+--------------------------------------+

What's Changed:

1. add a new memory table named region_label in information_schema to show the label rules
2. add GetAllLabelRules to retrieve all rules

Check List

Tests

• Unit test

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Yisaer
• xhebox

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[rleungx]

/cc @xhebox @Yisaer @JmPotato

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[xhebox]

Plz reping me after the other PR merged.

[Yisaer]

I think the region_label table is not proper for tidb while it is more suitable to display by PD. As region label is designed for table, I think it should be more proper to display label in infoschema.table

[xhebox]

I think the region_label table is not proper for tidb while it is more suitable to display by PD. As region label is designed for table, I think it should be more proper to display label in infoschema.table

@rleungx Do we have an agreement on the behavior now?

[rleungx]

PTAL @Yisaer

[xhebox]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 77bfbc7

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