planner: remove duplicate offset when push down pure limit down across outer join

[winoros]

What problem does this PR solve?

Issue Number: close #59926, to fix bug caused by #56483

Problem Summary:

What changed and how does it work?

in the pull #57471, we deal with the wrong case when there's order by. but doesn't fix the case if there's only a limit.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

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

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

修复当下推带有 OFFSET 没有 ORDER BY 子句的 LIMIT 至 JOIN 条件为 UNIQUE 而且内包含 NOT NULL 限制的 OUTER JOIN 下方时，结果可能出错的问题
Fix the issue that the result may be wrong when pushing down a limit that has an offset but doesn't have an order by clause down across an outer join, which join key is a unique key with the not null constraint.

[AilinKid]

How about desc the explain result, in the before case the top limit will be eliminated here

tidb> explain select * from t t1 left join t t2 on t1.a=t2.a limit 1, 1;
+----------------------------------+---------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------+
| id                               | estRows | task      | access object | operator info                                                                                                                        |
+----------------------------------+---------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------+
| Limit_14                         | 1.00    | root      |               | offset:1, count:1                                                                                                                    |
| └─IndexJoin_19                   | 1.25    | root      |               | left outer join, inner:TableReader_16, left side:Limit_26, outer key:test.t.a, inner key:test.t.a, equal cond:eq(test.t.a, test.t.a) |
|   ├─Limit_26(Build)              | 1.00    | root      |               | offset:1, count:1                                                                                                                    |
|   │ └─TableReader_30             | 2.00    | root      |               | data:Limit_29                                                                                                                        |
|   │   └─Limit_29                 | 2.00    | cop[tikv] |               | offset:0, count:2                                                                                                                    |
|   │     └─TableFullScan_28       | 2.00    | cop[tikv] | table:t1      | keep order:false, stats:pseudo                                                                                                       |
|   └─TableReader_16(Probe)        | 1.00    | root      |               | data:TableRangeScan_15                                                                                                               |
|     └─TableRangeScan_15          | 1.00    | cop[tikv] | table:t2      | range: decided by [test.t.a], keep order:false, stats:pseudo                                                                         |
+----------------------------------+---------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------+
8 rows in set (0.00 sec)

[tiprow]

@winoros: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
fast_test_tiprow	a0fbdcb	link	true	/test fast_test_tiprow

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[ti-chi-bot]

@winoros: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/build	a0fbdcb	link	true	/test build
idc-jenkins-ci-tidb/check_dev	a0fbdcb	link	true	/test check-dev
idc-jenkins-ci-tidb/unit-test	a0fbdcb	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	a0fbdcb	link	true	/test check-dev2

Full PR test history. Your PR dashboard.

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[elsa0520]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AilinKid, elsa0520

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-03-05 15:14:23.618495673 +0000 UTC m=+454576.747415418: ☑️ agreed by AilinKid.
• 2025-03-06 02:43:12.166443298 +0000 UTC m=+495905.295363042: ☑️ agreed by elsa0520.