How to modify SQL queries in order to guarantee sure answers

@article{Klein1994HowTM,
  title={How to modify SQL queries in order to guarantee sure answers},
  author={Hans-Joachim Klein},
  journal={SIGMOD Rec.},
  year={1994},
  volume={23},
  pages={14-20}
}
  • H. Klein
  • Published 1 September 1994
  • Computer Science
  • SIGMOD Rec.
Some problems connected with the handling of null values in SQL are discussed. A definition of sure answers to SQL queries is proposed which takes care of the “no information” meaning of null values in SQL. An algorithm is presented for modifying SQL queries such that answers are not changed for databases without null values but sure answers are obtained for arbitrary databases with standard SQL semantics. 
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