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Real OLAP queries usually don't have JOINs. Instead, the data is denormalized at ingestion nad WINDOW, CTE ans subqueries are used at query time.
by buremba 9y ago
Real OLAP queries usually don't have JOINs. Instead, the data is denormalized at ingestion nad WINDOW, CTE ans subqueries are used at query time.
- georgewfraser 9y agoThis was true 10 years ago. Many people building data warehouses today just use a normalized schema and write views with lots of joins. It’s a much simpler workflow and data warehouses have gotten so fast that this actually works.
- buremba 9y agoI don't know any technology that makes the JOINs efficient enough for low latency queries. If you're joining two tables that have billions of rows, you need too much memory and CPU resources in order to be able to map them. Do you know any DBMS that focuses on OLAP systems and suggest normalization?
- StreamBright 9y agoI can just second that. Most DWHs arr denormalized because columnar storage formats love repetition.