MAP_AGG for key-value pairs

Concepts covered: sqlMapAgg

MAP_AGG Fundamentals Basic Syntax Practical Example Consider a product configuration table: Each product now has a single row with all its settings in a map. Downstream code can access settings.color or settings.size directly without parsing. ARRAY_AGG vs MAP_AGG Choose the right aggregation based on your access pattern: Accessing Map Values If duplicate keys exist within a group, the last value wins. Ensure your data has unique keys per group or use deduplication first.

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.

How DataDriven Lessons Work

DataDriven combines four interview rounds (SQL, Python, Data Modeling, Pipeline Architecture) with adaptive difficulty and spaced repetition. Easy problems get harder as you improve. Weak concepts resurface until you master them. Your readiness score tracks progress across every topic interviewers test. Every lesson section ends with problems you solve by writing and running real code, not by picking multiple-choice answers.