ARRAY_AGG for collecting values

Concepts covered: sqlArrayAgg

ARRAY_AGG Fundamentals Basic Syntax For each customer, this collects all their order IDs into a single array. The result is an array type that can be processed by other functions. Practical Example Consider an orders table: Each customer appears once with all their products collected in an array. The array preserves each individual value. Arrays vs Strings Arrays provide significant advantages over comma-separated strings for storing collected values. Why Arrays Beat Strings Arrays preserve structure in a way that comma-separated strings cannot. Arrays as Strings Which approach preserves type information when collecting values?

About This Interactive Section

This section is part of the Aggregating: 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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