Data analyst shares six SQL query patterns to detect transaction fraud: velocity checks, impossible travel detection, amount anomalies, merchant clusters, off-hours purchases using window functions.

Six SQL patterns I use to catch transaction fraud

May 12, 2026 Quick disclaimer: I do data work on a program-integrity team. Examples below use generic transaction tables and made-up scenarios. Nothing here comes from anything I’ve actually worked on or seen. Views are mine, not my employer’s. Fraud detection in transaction data is mostly SQL. Not machine learning, not graph databases, not whatever Gartner is hyping this year. SQL, run against the right tables, with the right joins, looking for the right shapes. I work mostly with government-...