planner: support stable result mode (#25971)

[ti-srebot]

cherry-pick #25971 to release-5.1
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/25995

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git push git@github.com:ti-srebot/tidb.git pr/25995:release-5.1-c24a90f9e7f5

---

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary: support stable result mode in the planner

What is changed and how it works?

Results of some queries are not stable, for example:

create table t (a int);
insert into t values (1), (2);
select a from t;

In the case above, the result can be 1 2 or 2 1, which is not stable.
This PR introduces a new switch that can make the results of these queries stable.

This feature is implemented as a logical optimization rule, which stabilizes results by modifying Sort in plans or inject new Sort into plans.
First, all operators are divided into 2 types:

1. input-order keepers: Selection, Projection, Limit;
2. all other operators.

The basic idea of this rule is:

1. iterate the plan from the root, and ignore all input-order keepers;
2. when meeting the first non-input-order keeper,
   2.1. if it's a Sort, complete it by appending its output columns into its order-by list,
   2.2. otherwise, inject a new Sort upon this operator.

Check List

Tests

• Unit test

Release note

• planner: support stable result mode

[ti-srebot]

/run-all-tests

[ti-srebot]

@qw4990 you're already a collaborator in bot's repo.

[qw4990]

/run-all-tests

[qw4990]

/run-all-tests

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Reminiscent
• time-and-fate

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[Reminiscent]

/merge

[ti-chi-bot]

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

Commit hash: 8408754