Yuanjia Zhang

planner: update SPM doc

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### First-time contributors' checklist - [ ] I've signed [**Contributor License Agreement**](https://cla-assistant.io/pingcap/docs-cn) that's required for repo owners to accept my contribution. ### What is changed, added or deleted? (Required) ###...

planner: add projections to keep join keys as `col=col`

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### What problem does this PR solve? Issue Number: close #46556 Problem Summary: planner: add projections to keep join keys as `col=col` ### What changed and how does it work?...

Unity

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### What problem does this PR solve? Issue Number: close #xxx Problem Summary: ### What changed and how does it work? ``` explain format='unity' select * from t1, t2 where...

planner: update the doc about Plan Cache

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### First-time contributors' checklist - [ ] I've signed [**Contributor License Agreement**](https://cla-assistant.io/pingcap/docs-cn) that's required for repo owners to accept my contribution. ### What is changed, added or deleted? (Required) ###...