# Summarization

* When we are aggregating data, we generally remove the detail data that lies below the summarize table.
* The whole point of aggregation is to replace detail data with summaries. This is where subtotals comes in!
* A grouping set is a set of columns by which you group.
* The PostgreSQL `ROLLUP` is a subclass of the GROUP BY clause that offers shorthand for defining '**multiple grouping sets**'