DBMS: Entity Integrity (Definitions)

"Within a table, each row describes an entity that is a member of the set kept in the table. Entity integrity ensures that each row in the table is uniquely identifiable." (Owen Williams, "MCSE TestPrep: SQL Server 6.5 Design and Implementation", 1998)

"Integrity that defines a row as a unique entity for a particular table and ensures that the column cannot contain duplicate values. It usually enforces the primary key of a table (through indexes, UNIQUE constraints, or PRIMARY KEY constraints)." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"Entity integrity refers to a state in which all the rows in a database have a non-null primary key value, all tables have primary keys, and no table has any duplicate primary key values. Entity integrity ensures there are no duplicate entries for anything represented in the database." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"A relational database integrity mechanism that ensures that duplicate rows do not exist in a table. Requiring that all rows in a table have a unique identifier." (Victor Isakov et al, "MCITP Administrator: Microsoft SQL Server 2005 Optimization and Maintenance (70-444) Study Guide", 2007)

"Integrity that defines a row as a unique entity for a particular table and ensures that the column cannot contain duplicate values." (S. Sumathi & S. Esakkirajan, "Fundamentals of Relational Database Management Systems", 2007)

"Requires that all tables have a primary key. The values in the primary key fields must be non-null and no two records can have the same primary key values." (Rod Stephens, "Beginning Database Design Solutions", 2008)

"A constraint on a relation that states that no part of the primary key can be null." (Jan L Harrington, "Relational Database Design and Implementation' 3rd Ed., 2009)

"The property of a relational table that guarantees that each entity has a unique value in a primary key and that there are no null values in the primary key." (Carlos Coronel et al, "Database Systems: Design, Implementation, and Management" 9th Ed., 2011)

"A state in which every row of every table can be uniquely identified." (Microsoft, "SQL Server 2012 Glossary", 2012)

"The most basic level of data integrity provided by relational databases stating that each occurrence of an entity must be uniquely identifiable." (Craig S Mullins, "Database Administration", 2012)