parser: support `show placement ...` syntax

[lcwangchao]

What problem does this PR solve?

Support syntax show placement ... see: https://github.com/pingcap/tidb/pull/26221

What is changed and how it works?

Support the below syntax:

SHOW PLACEMENT [LIKE 'pattern' | WHERE expr]
SHOW PLACEMENT FOR [{DATABASE | SCHEMA} schema_name] [TABLE table_name [PARTITION partition_name]];

Same examples:

SHOW PLACEMENT;
+----------------------------+----------------------------------------------------------------------+------------------+
| target                     | placement                                                            | scheduling_state |
+----------------------------+----------------------------------------------------------------------+------------------+
| POLICY system              | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2" FOLLOWERS=4 | SCHEDULED        |
| POLICY default             | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2"             | SCHEDULED        |
| DATABASE test              | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2"             | SCHEDULED        |
| TABLE test.t1              | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2"             | SCHEDULED        |
| TABLE test.t1 PARTITION p1 | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2"             | INPROGRESS       |
+----------------------------+----------------------------------------------------------------------+------------------+
5 rows in set (0.00 sec)

SHOW PLACEMENT LIKE 'POLICY%';
+----------------------------+----------------------------------------------------------------------+------------------+
| target                     | placement                                                            | scheduling_state |
+----------------------------+----------------------------------------------------------------------+------------------+
| POLICY system              | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2" FOLLOWERS=4 | SCHEDULED        |
| POLICY default             | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2"             | SCHEDULED        |
+----------------------------+----------------------------------------------------------------------+------------------+
2 rows in set (0.00 sec)

SHOW PLACEMENT FOR DATABASE test;
+----------------------------+----------------------------------------------------------------------+------------------+
| target                     | placement                                                            | scheduling_state |
+----------------------------+----------------------------------------------------------------------+------------------+
| DATABASE test              | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2"             | SCHEDULED        |
| TABLE test.t1              | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2"             | SCHEDULED        |
| TABLE test.t1 PARTITION p1 | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-east-2"             | INPROGRESS       |
+----------------------------+----------------------------------------------------------------------+------------------+
3 rows in set (0.00 sec)

Check List

Tests

• Unit test

Related changes

• N/A

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• morgo
• xhebox

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All committers have signed the CLA.

[xhebox]

/cc @morgo @djshow832