On the Codd semantics of SQL nulls

作者：

Highlights：

• SQL nulls are commonly interpreted as non-repeating marked nulls, but even simple queries may produce answers that break this interpretation.

• The class of queries preserving the Codd interpretation of SQL nulls cannot be captured syntactically.

• Sufficient syntactic restrictions for preservation can be obtained by leveraging NOT NULL constraints on the database schema.

摘要

•SQL nulls are commonly interpreted as non-repeating marked nulls, but even simple queries may produce answers that break this interpretation.•The class of queries preserving the Codd interpretation of SQL nulls cannot be captured syntactically.•Sufficient syntactic restrictions for preservation can be obtained by leveraging NOT NULL constraints on the database schema.

论文关键词：SQL,Null,Semantics,Relational database

论文评审过程：Received 30 March 2018, Accepted 13 August 2018, Available online 16 August 2018, Version of Record 30 July 2019.

论文官网地址：https://doi.org/10.1016/j.is.2018.08.001