docs/design: add proposal for recursive common table expression (CTE) #19253
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| - Author(s): [Pingyu](https://github.com/pingyu) (Ping Yu) | ||
| - Last updated: 2020-08-18 | ||
| - Discussion at: https://github.com/pingcap/tidb/issues/17472 | ||
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| CTEs depending on other CTE(s) begins to execute after the dependencies are all met. Independent CTEs can execute parallel. | ||
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| ## Rationale | ||
| MariaDB[4] build a dependency matrix in preparatory stage to detect recursive CTEs, check seed parts, and determine dependency between CTEs. |
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it's better to add more content about how recursive common table expression is implemented in other DBMS like what we did in the proposal of non-recursive common table expression.
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| ## Background | ||
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| From MySQL User Document, [13.2.15 WITH (Common Table Expressions)](https://dev.mysql.com/doc/refman/8.0/en/with.html): |
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It's better to describe more about the usage of recursive CTE like what we did in the proposal of non-recursive CTE.
| ## Implementation | ||
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| ### Temporary Table | ||
| Temporary table is implemented by `chunk.RowContainer`, which stores tuples in memory, or spill to disk if exceeds memory quota. |
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Is it possible to share the same code which implements the temporary table described in #1248?
| ## Proposal | ||
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| ### Seed part & Recursive part | ||
| Recursive CTE has two parts, seed part and recursive part, separated by `UNION ALL` or `UNION [DISTINCT]`. |
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It's better to introduce the syntax of recursive CTE beforing explaining what are seed, union all, and recursive parts.
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I'm going to close this PR since it hasn't been updated for a long time. feel free to reopen if you want to continue with it. thank you for your contribution. |
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The design doc is great, and we need to continue to finish the implementation of recursive CTE. |
That's great ! |
What problem does this PR solve?
Issue Number: #17472 #6824
Problem Summary:
What is changed and how it works?
Proposal: Recursive Common Table Expression
What's Changed:
(TBD)
How it Works:
(TBD)
Related changes
pingcap/docs/pingcap/docs-cn: (TBD)Check List
Tests
(TBD)
Side effects
(TBD)
Release note