planner: donot prune all columns for Projection (#24024)

[ti-srebot]

cherry-pick #24024 to release-5.0
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---

Signed-off-by: guo-shaoge shaoge1994@163.com

What problem does this PR solve?

Issue Number: close #23887

Problem Summary:

Hash Join (eq("abc", tbl1.col1))
  |                     |
Projection     DataSource(tbl1)
  |
Index Join

1. We prune all columns in Projection
2. Resolve indices for col1, Its index is 0(because Projection's output columns are all pruned)
3. Projection is eliminated, because its output columns are all pruned. But Index Join still has output columns
4. Got panic when calc eq("abc", tbl1.col1). Because use index 0 to eval tbl1.col1

What is changed and how it works?

What's Changed:

1. We donot prune all columns in Projection. If Projection is pruned to empty, we make it a Projection 1 (just like count(1))
2. Delete some code in rule_eliminate_projection.go, because Projection cannot be empty. Check here

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Integration test

Side effects: no

Release note

• donot prune all columns for Projection

[ti-srebot]

/run-all-tests

[ti-srebot]

@guo-shaoge you're already a collaborator in bot's repo.

[ti-chi-bot]

@wshwsh12: /merge in this pull request requires 2 /lgtm.

In response to this:

/merge

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lzmhhh123
• winoros

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[guo-shaoge]

/run-all-tests

[lzmhhh123]

/merge

[ti-chi-bot]

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

Commit hash: 5100a75

[winoros]

/merge

[guo-shaoge]

/run-integration-common-test

[ti-chi-bot]

@ti-srebot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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[zhouqiang-cl]

/run-integration-tests