DBMS: NULL (Definitions)

"Having no explicitly assigned value. NULL is not equivalent to zero, or to blank. A value of NULL is not considered to be greater than, less than, or equivalent to any other value, including another value of NULL." (Karen Paulsell et al, "Sybase SQL Server: Performance and Tuning Guide", 1996)

"An entry that has no explicitly assigned value. NULL is not equivalent to zero or blank. A value of NULL is not considered to be greater than, less than, or equivalent to any other value, including another value of NULL." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"A possible value for any Oracle column that indicates the absence of any known value for that column. A NULL is usually used to represent a value that is unknown, not applicable, or not available." (Bob Bryla, "Oracle Database Foundations", 2004)

"A special column value that means 'this column has no value'." (Rod Stephens, "Beginning Database Design Solutions", 2008)

"Null is a special marker used to indicate an unknown value or the absence of a value within a database." (Michael Coles & Rodney Landrum, , "Expert SQL Server 2008 Encryption", 2008)

"An entry that has no explicitly assigned value. null is not the same as zero or blank." (Jim Joseph, "Microsoft SQL Server 2008 Reporting Services Unleashed", 2009)

"A value, distinct from 0 or a blank, that means 'unknown'." (Jan L Harrington, "SQL Clearly Explained 3rd Ed. ", 2010)

"Pertaining to a value that indicates missing or unknown data." (Microsoft, "SQL Server 2012 Glossary", 2012)

"Represents missing or unknown information at the attribute (or column) level. If an attribute (or column) 'value' can be null, it can mean one of two things: The attribute/column is not applicable for certain occurrences of the entity, or the attribute applies to all entity occurrences, but the information may not always be known. It could be a combination of these two situations, too." (Craig S Mullins, "Database Administration", 2012)

"Having no explicitly assigned value. NULL is not equivalent to zero, or to blank. A value of NULL is not considered to be greater than, less than, or equivalent to any other value, including another value of NULL." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)