This is the second one of three blogs to introduce TiDB internal.
This is the first one of three blogs to introduce TiDB internal.
This is the speech Siddon Tang gave at the 1st Rust Meetup in Beijing on April 16, 2017.
The target audience of this document is the contributors in the TiDB community. The document aims to help them understand the TiDB project. It covers the system architecture, the code structure, and the execution process.
Subquery optimization, especially rewriting the correlated subquery, is a very difficult part in SQL query optimization. To be compatible with MySQL, TiDB enables users to write subqueries anywhere they want. For those subqueries that are not correlated, which are also called uncorrelated subqueries, TiDB evaluates in advance; for those correlated subqueries, TiDB removes the correlations as much as possible. For example, TiDB can rewrite a correlated subquery to `SemiJoin`. This article is focused on introducing the correlated subquery optimization methods in TiDB.
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