planner: fix index merge union case couldn't sink limit into index merge reader

[AilinKid]

What problem does this PR solve?

Issue Number: close #48588

Problem Summary:

What is changed and how it works?

detail ref the comment #48588 (comment) in the issue above

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.

planner: fix index merge union case couldn't sink limit into index merge reader

[tiprow]

Hi @AilinKid. Thanks for your PR.

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[codecov]

Codecov Report

Merging #48590 (b25c240) into master (4793a04) will increase coverage by 1.6850%.
Report is 16 commits behind head on master.
The diff coverage is 71.4285%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #48590        +/-   ##
================================================
+ Coverage   71.4227%   73.1078%   +1.6850%     
================================================
  Files          1404       1428        +24     
  Lines        407209     415854      +8645     
================================================
+ Hits         290840     304022     +13182     
+ Misses        96403      92955      -3448     
+ Partials      19966      18877      -1089     

Flag	Coverage Δ
integration	44.1905% <71.4285%> (?)
unit	71.6961% <71.4285%> (+0.2733%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9874% <ø> (ø)
parser	∅ <ø> (∅)
br	48.8241% <ø> (-4.2517%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qw4990, winoros

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-14 11:36:09.84010237 +0000 UTC m=+4162567.427212514: ☑️ agreed by winoros.
• 2023-11-15 06:19:33.275696056 +0000 UTC m=+4229970.862806186: ☑️ agreed by qw4990.

[AilinKid]

/ok-to-test

[AilinKid]

/retest

[AilinKid]

/retest-required

[AilinKid]

/test unit-test

[tiprow]

@AilinKid: The specified target(s) for /test were not found.
The following commands are available to trigger required jobs:

• /test tiprow_fast_test

Use /test all to run all jobs.

In response to this:

/test unit-test

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[hawkingrei]

/retest

[AilinKid]

/test unit-test

[tiprow]

@AilinKid: The specified target(s) for /test were not found.
The following commands are available to trigger required jobs:

• /test tiprow_fast_test

Use /test all to run all jobs.

In response to this:

/test unit-test

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #48632.