SQL's Three-Valued Logic and Certain Answers

  title={SQL's Three-Valued Logic and Certain Answers},
  author={Leonid Libkin},
  journal={ACM Trans. Database Syst.},
The goal of the article is to bridge the difference between theoretical and practical approaches to answering queries over databases with nulls. Theoretical research has long ago identified the notion of correctness of query answering over incomplete data: one needs to find certain answers, which are true regardless of how incomplete information is interpreted. This serves as the notion of correctness of query answering, but carries a huge complexity tag. In practice, on the other hand, query… CONTINUE READING
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