Launch HN: Datafold (YC S20) – Diff Tool for SQL Databases
It is always good to see new approaches to testing but I don&#x27;t see how this one is going to work. I&#x27;ve worked at multiple database companies. Diff&#x27;ing data is one of the weakest and most cumbersome ways to verify correctness.<p>Diffs are relatively slow, when they fail you get a blizzard of errors, and the oracles (i.e. the &quot;good&quot; output) have to be updated constantly as the product changes. Plus I don&#x27;t see how this helps with schema migration or performance issues, which are major problems in data management. And don&#x27;t get me started on handling things like dates, which change constantly, hence break diffs.<p>If you really care about correctness it&#x27;s better to use approaches like having focused test cases that check specific predicates on data. They can run blindingly fast and give you actionable data about regressions. They&#x27;re also a pain to code but are most productive in the long run.