v.18.12Improvement

Improved PREWHERE Performance and Expression Transfer

Official CH changelog text
Improved performance when using PREWHERE and with implicit transfer of expressions in PREWHERE.
Improved performance in ClickHouse queries by optimizing the use of PREWHERE clauses along with implicit transfer of expressions within PREWHERE.

Why it matters

This feature aims to enhance query execution efficiency by better leveraging the PREWHERE clause to filter data earlier and more effectively. Implicit transfer of expressions allows more conditions to be applied at the PREWHERE stage without requiring manual rewriting, thereby reducing the amount of data processed and improving overall query performance.

How to use it

Users can benefit from this improvement by continuing to use PREWHERE in their queries as before. The system now implicitly transfers relevant expressions into the PREWHERE clause automatically, requiring no additional changes in query syntax.
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