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ACM SIGMOD Record, 2008
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".
John Grant
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Nulls, three-valued logic, and ambiguity in SQL

ACM SIGMOD Record, 2007
Date's popular critique of SQL's three-valued logic [4, 3] purports to demonstrate that SQL queries can produce erroneous results when nulls are present in the database. I argue that this critique is flawed in that Date misinterprets the meaning of his example query.
Claude Rubinson
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NULL-Werte und dreiwertige Logik in SQL

, 1992
In relationalen Datenbanken ist es ublich, das gewisse Felder „NULL“ sein konnen (vgl. [Date86]). Wir sagen hier bewust nicht „den Wert NULL haben“. NULL kann u.a. bedeuten, das der aktuelle Wert eines Attributs unbekannt ist. Andere Arten von Nullen, wie z.B. „nicht anwendbar“ oder „gibt es nicht“ werden hier nicht behandelt, (vgl.
Günter Matthiessen
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A critique of Claude Rubinson's paper nulls, three - valued logic, and ambiguity in SQL

ACM SIGMOD Record, 2008
I’d like to thank Claude Rubinson for his thoughtful critique [3] of my remarks in reference [1] on nulls and three-valued logic (3VL). Clearly we’re in agreement on the major issues; as Rubinson says, “I agree with Date that three-valued logic is incompatible with database management systems.” We also agree that null isn’t a value; as Rubinson says ...
C. J. Date
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NULLs—Missing Data in SQL

, 2015
Joe Celko
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Handling Null Values in SQL Queries on Relational Databases