UNNEST for Array Expansion

Basic UNNEST Filtering Unnested Data This filters the unnested items to include only those containing "premium". The result shows only matching items with their order IDs. Aggregating Unnested Arrays After unnesting, standard aggregation functions work on the expanded rows. This counts total item occurrences and unique items across all orders. UNNEST vs Lambda Functions After unnesting, you can group by the original row identifier to recollect elements, or apply aggregations across all elements from all rows together.

About This Interactive Section

This section is part of the Complex Data: Advanced lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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