planner: do not build MPP plan for scan with virtual columns (#23980)

[ti-srebot]

cherry-pick #23980 to release-5.0
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git pr https://github.com/pingcap/tidb/pull/24058

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---

What problem does this PR solve?

Issue Number: close #23886

Problem Summary:

Planner reports resolve index failure for MPP plan on virtual columns.

What is changed and how it works?

What's Changed:

Avoid generating MPP plan when the scan contains virtual columns.

How it Works:

If we enable MPP plan for such kind of cases, we need to add an extra projection node above to prune the newly appended columns, as what we do for copTask, otherwise we would get wrong query results. However, for a MPP task, we may attach plan nodes such as projection, hash aggregation and hash join upon the scan node, which would change the schema of the plan tree, so we have no idea of the target schema that the plan tree should be projected to then. Unlike copTask in which the PhysicalTableReader is the counterpart of DataSource, so we can add the projection upon the PhysicalTableReader, while in mppTask, the PhysicalTableReader is acting more like a data receiver, instead of the counterpart of the DataSource.

Meanwhile, I am not sure whether MPP execution engine can handle plan snippets which contain virtual columns, since I noticed that in addPushedDownSelectionToMppTask, no MPP task would be produced if the pushed down filter contains virtual columns.

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test

Side effects

N/A

Release note

• Do not build MPP plan for scan with virtual columns

[ti-srebot]

/run-all-tests

[ti-srebot]

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

[eurekaka]

/run-integration-compatibility-test

[time-and-fate]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• time-and-fate
• winoros

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[zz-jason]

/merge

[ti-chi-bot]

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

Commit hash: 5b28dfe

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