What is 'Columnar Aggregation'?

What is 'Columnar Aggregation'?

Approach: Explain why summing a column is fast in columnar formats.

The ability of a columnar database to perform math on a column by reading values sequentially from a single contiguous block of memory/disk, avoiding row-traversal overhead.

Follow-up: Is it faster for COUNT(*) or SELECT *?

Key concepts: sequential access, cpu efficiency.