Zhou Kunqin

understand-tidb: add rbo section

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### What issue does this PR solve? - close #59 ### What is changed: Add the Rule-based Optimization section.

This repo doesn't have a license now. We need to choose a license for it.

parser, planner: add query block level `no_decorrelate` hint (#37633)

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### What problem does this PR solve? Issue Number: ref #37789 Problem Summary: ### What is changed and how it works? ### Check List Tests - [x] Unit test -...

optimizer-hints, correlated-subquery-optimization: add docs for `no_decorrelate` hint

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### What is changed, added or deleted? (Required) Add description for the new `no_decorrelate` hint, and update some descriptions for the correlated subquery. This is expected for v6.4.0. ### Which...

optimizer-fix-controls, explain-index-merge: add optimizer fix control 52869 for index merge

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### What is changed, added or deleted? (Required) ### Which TiDB version(s) do your changes apply to? (Required) **Tips for choosing the affected version(s):** By default, **CHOOSE MASTER ONLY** so...

large overestimation when where conditions contain OR and matches several indexes with different selectivity

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## Reproduce ```sql create table t(a int, b int, c int, d int, index iabc(a,b,c), index ib(b)); -- run this many times insert into t value (rand()*100000, rand()*10, rand()*1000, rand()*1000),(rand()*100000,...

planner: fix incorrect maintenance of `handleColHelper` for recursive CTE

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### What problem does this PR solve? Issue Number: close #55666 Problem Summary: ### What changed and how does it work? ### Check List Tests - [ ] Unit test...