First Normal Form (1NF)

Concepts covered: dmFirstNormalForm

1NF: No Lists in Cells A table is in first normal form when every cell contains a single atomic value. No comma-separated lists. No arrays stored as strings. No multiple values crammed into one column. This sounds obvious, but 1NF violations are everywhere in real data. A tags column with 'python, sql, spark'. A phone_numbers column with '555-1234, 555-5678'. These break filtering, indexing, and joining. Here is a 1NF violation: You cannot filter for 'students taking Physics' without string parsing. You cannot count courses per student without splitting on commas. You cannot join to a courses table because the FK is a comma-separated string, not a single value. The fix: one row per student-course combination.

About This Interactive Section

This section is part of the Normalization 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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