Why storing '2026-27' as a database key beats computing date ranges each time

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A software developer writing for DEV Community explains a database design decision made while building a school and university discount redemption system. Rather than computing academic year date ranges dynamically on every query, each redemption row is stored with a short string key like '2026-27' representing the academic year it belongs to. This approach turns cap-usage checks into fast, indexed equality lookups instead of timestamp range scans. More importantly, it preserves historical accuracy: if the academic year start month is ever changed, stored period keys ensure past redemptions are not silently reclassified. The author draws a parallel to storing the price paid on an order row, arguing that any fact tied to a decision should be recorded at the moment it is made, not recomputed from rules that may later change.

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