Department of Computer, Control and Management Engineering

Multiple surveys show that SQL and relational databases remain the most common tools used by data scientists. But can we fully trust them? We give a few examples showing unexpected and counterintuitive behavior of even simple SQL queries that make one question analytics results obtained from relational DBMSs. The talk will then give a quick overview of two lines of work that attempt to overcome these problems. One concerns a formal semantics of SQL, to at least eliminate the element of surprise in query results. The other presents a revised evaluation scheme that restores correctness to the notoriously unpredictable behavior of SQL queries over databases with incomplete information.