planner,executor: fix cached table query with filter condition

[tiancaiamao]

What problem does this PR solve?

Issue Number: close #32422

Problem Summary:

This bug was introduced by #32139
In the initial implementation, I generate UnionScan plan when reading from cache, and no UnionScan when the cache is bypassed or unavailable.
But since the shape of the plan is different, the prepared plan cache feature is not applicable.

Then, #32139 try to fix the prepare plan cache issue by defer the UnionScanExec generation to the executor build phase. It did make plan cache possible, but introduce bug #32422

Handling the filter condition is not a trivial work if we continue generating UnionScanExec in the executor build phase:

• In the logical plan phase, by the predication push down optimize rule, the condition is seperated.
  Some are pushed down to TableReader and some remains, cause it's difficult to rebuild the filter condition for UnionScan in the executor build phase.
• And also the existence of generated column make the situation from bad to worse.

What is changed and how it works?

So I change the implementation the third time.
This time, I will always keep the UnionScan in the planner phase for a cached table, and whether the UnionScan is really used is decided by whether the cached data is available.

In this way, prepared plan cache is applicable, since the shape of plan is unchanged (although maybe less efficient in some minor cases), and also the filter condition bug is fixed.

Check List

Tests

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

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lcwangchao
• tangenta

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[tiancaiamao]

/rebuild

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/c2a28e663d7ff4752516359a2d43f4da6fd4d593

[ti-chi-bot]

@tiancaiamao: PR needs rebase.

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[tiancaiamao]

/merge

[ti-chi-bot]

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

Commit hash: 93331c8

[tiancaiamao]

/run-unit-test

[tiancaiamao]

/run-mysql-test