The Problem of Identity

Without a reliable way to uniquely identify each row, queries produce wrong results. Joins multiply rows. Updates touch the wrong records. Deletes wipe related data. The entire relational model depends on every row being unambiguously identifiable. Keys are how you provide that guarantee. Natural vs Surrogate Keys A natural key uses data that already exists in the business domain: an email address, a product SKU, a government ID number. A surrogate key is a system-generated identifier with no business meaning. Both have real tradeoffs, and the right choice depends on the specific table and how it will be used downstream. The choice is not 'surrogate keys are always better.' It is situational. For a patient record system, HIPAA-regulated IDs change when patients move regions, so a surrogate