The Halloween Problem: a spooky (and true) SQL story

The Halloween Problem is a phenomenon in relational databases where certain SQL operations like INSERT, UPDATE, DELETE, and MERGE can unintentionally result in multiple updates to the same row, potentially causing infinite loops. This issue was first identified by Don Chamberlin, Patricia Selinger, and Morton Astrahan in the 1970s, and it highlights how a non-clustered index can disrupt the logical order of data entries during a write operation. The problem was named after Halloween due to its discovery date, and although modern database systems incorporate strategies like query optimizers to mitigate such issues, the Halloween Problem remains a cautionary tale for database users. It underscores the importance of understanding a database management system's capabilities and limitations to prevent performance impacts or unexpected behaviors.