A flat schema stores one value per column, so queries read like plain SQL. A nested schema packs repeated key-value pairs inside a single column.
GA4’s BigQuery export stores event parameters nested in event_params, so almost every query starts with UNNEST.
Why It Matters
Flat tables are faster to write queries against, easier for BI tools, and far easier for AI agents to query correctly.
In d8a.tech
Events and sessions are written as flat columns, and custom parameters can be mapped to their own columns.