Constraints on null values in relational databases

Authors:
Billie S. Goldstein
Affiliations:
-
Venue:
VLDB '81 Proceedings of the seventh international conference on Very Large Data Bases - Volume 7
Year:
1981

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Abstract

If null values are allowed in a database, the database designer may want to restrict where they occur. Two constructs are presented for specifying where null values may occur in a relational database. Several examples demonstrate the use of these two techniques. The two constructs are shown to be almost equivalent; a criterion for exact equivalence is given. Under the same criterion, interesting special cases of both constructs are also shown to be equivalent.