Projections in ClickHouse
Mark Needham
Discover how to dramatically improve query performance in ClickHouse using projections - a powerful feature that creates query-optimized copies of your data.
This video demonstrates projections using a real-world example with 30 million UK property price records. Watch as we reduce query time from 53 milliseconds to just 4 milliseconds by creating a projection for calculating average house prices by county.
What You'll Learn:
- What projections are and how they work as hidden tables that update atomically
- Three main use cases: reordered datasets, subset of columns filtering, and pre-computed aggregations
- Step-by-step process to create and materialize projections
- How to verify projections are being used with EXPLAIN queries
- Understanding the storage trade-offs and space requirements
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