Dates Hide in Every Business Question

Concepts covered: sqlDateTrunc

The four-tool date toolkit Four functions cover 90% of date arithmetic in production SQL. DATE_TRUNC truncates a date or timestamp to a coarser unit; DATE_TRUNC('month', '2024-03-15') returns '2024-03-01.' This is the workhorse for grouping. INTERVAL arithmetic adds or subtracts time spans; CURRENT_DATE - INTERVAL '30 days' returns the date 30 days ago. This is the workhorse for windowing. EXTRACT pulls a part out of a date or timestamp; EXTRACT(YEAR FROM txn_date) returns 2024. This is the workhorse for filtering by year/month/dow. DATE_DIFF computes the difference between two dates in a specified unit; DATE_DIFF('day', signup_date, CURRENT_DATE) returns the days since signup. This is the workhorse for age and tenure. Why companies care Date arithmetic is the most error-prone area of prod

About This Interactive Section

This section is part of the Date Arithmetic: Beginner 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 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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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.