Partition Pruning on Date Columns

Concepts covered: sqlComplexPatterns

Fiscal calendars are not static. Companies restructure their fiscal years (Apple moved its fiscal year-end from June to September in the 1980s and again later; many retailers shift to 4-4-5 calendars as they grow). When the calendar changes, the historical reports under the old calendar are still valid for the period they cover; the new calendar applies only going forward. The naive approach (update the calendar table in place) breaks historical reproducibility. The right approach is a versioned calendar with SCD-2 semantics. The SCD-2 calendar table How the fiscal restructure is recorded When the fiscal calendar changes, the platform inserts new rows into dim_calendar_versioned with new effective_from dates and supersedes the old rows by setting their effective_to. Historical queries that

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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.

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