Aggregation

Raw data is usually rows of individual events: one order, one click, one transaction. Business questions, on the other hand, are usually about summaries.

• "What's our total revenue by region?"
• "How many orders did each customer place?"
• "What's the average order value by product category?"

You don't answer these by reading individual rows, but rather by aggregating: grouping rows together and calculating summary statistics. Common aggregations include:

• Sums
• Medians
• Counts
• Averages
• Minimums and maximums
• etc

Aggregations take you from 10,000 "raw" order rows to 50 category-level summaries.