Null values in SQL

ABSTRACT

In various writings over the past 20 years, such as [3], Date has pointed out that SQL produces incorrect answers to some queries where a null value is included in a table. In a recent article in the ACM SIGMOD Record, [8], Rubinson states that "Date misinterprets the meaning of his example query" and "SQL returns the correct answer to the query posed". The purpose of this article is to show that, contrary to Rubinson's claim, Date's critique of query evaluation in the presence of null values in SQL is completely justified.

REFERENCES

• 1: E.F. Codd. Understanding relations (installment #7). FDT Bulletin of ACM-SIGMOD, 7(3-4):23--28, 1975.
• 2: C. J. Date, An introduction to database systems (7th ed.), Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 1999
• 3: C. J. Date, An introduction to database systems (7th ed.), Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 1999
• 4: J. Grant. A non-truth-functional 3-valued logic. Mathematics Magazine, 47(4):221--223, September-October 1974.
• 5: J. Grant. Null values in a relational data base. Information Processing Letters, 6(5):156--157, October 1977.
• 6: Jorge Lobo , Jack Minker , Arcot Rajasekar, Foundations of disjunctive logic programming, MIT Press, Cambridge, MA, 1992
• 7: David Maier, Theory of Relational Databases, Computer Science Pr, 1983
• 8: Claude Rubinson, Nulls, three-valued logic, and ambiguity in SQL: critiquing date's critique, ACM SIGMOD Record, v.36 n.4, p.13-17, December 2007 [doi>10.1145/1361348.1361350]
• 9: Dan Suciu , Nilesh Dalvi, Foundations of probabilistic answers to queries, Proceedings of the 2005 ACM SIGMOD international conference on Management of data, June 14-16, 2005, Baltimore, Maryland [doi>10.1145/1066157.1066303]

INDEX TERMS

Primary Classification:
  H. Information Systems
  H.2 DATABASE MANAGEMENT
      H.2.3 Languages

          Nouns: SQL

Additional Classification:
  H. Information Systems
  H.2 DATABASE MANAGEMENT
      H.2.1 Logical Design

General Terms:
Design, Languages, Reliability