Calendar Tables and Holiday-Aware Math

Concepts covered: sqlTimestampType

The bitemporal table The two reproducibility queries Two query shapes operate on a bitemporal table. The as-of-business-time query asks: 'what was the transaction's correct value at business time T?' This is the standard reporting query, with corrections applied. The as-of-system-time query asks: 'what did the system believe was the transaction's value as of system time S?' This is the reproducibility query, used for audit and regulatory reporting. The two queries can produce different numbers for the same transaction if a correction was applied between the business event and the audit date. The audit use case Regulated industries (financial services, healthcare, ad tech) must reproduce historical reports exactly. A regulator asks: 'show me the January report exactly as it was when you pub

About This Interactive Section

This section is part of the Date Arithmetic: 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 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.