🛢DBMS: Primary Key [PK] (Definitions)

"The column or columns whose values uniquely identify a row in a table." (Karen Paulsell et al, "Sybase SQL Server: Performance and Tuning Guide", 1996)

"The column or combination of columns that uniquely identifies a table. It must always be non-null and will always have a unique index. A primary key is used for joins with foreign keys in other tables." (Patrick Dalton, "Microsoft SQL Server Black Book", 1997)

"A column (or columns) in a table that makes the row in the table distinguishable from every other row in the same table." (Bob Bryla, "Oracle Database Foundations", 2004)

"A column or set of columns that uniquely identify all the rows in a table." (Thomas Moore, "EXAM CRAM™ 2: Designing and Implementing Databases with SQL Server 2000 Enterprise Edition", 2005)

"A unique attribute used to identify a single record in a database." (William H Inmon, "Building the Data Warehouse", 2005)

"This is an index that ensures that each of the records in your table is unique in  some way." (Joseph L Jorden & Dandy Weyn, "MCTS Microsoft SQL Server 2005: Implementation and Maintenance Study Guide - Exam 70-431", 2006)

"A candidate key that is singled out as the table's 'main' method for uniquely identifying records. Most databases automatically build an index for a table's primary key and enforce uniqueness." (Rod Stephens, "Beginning Database Design Solutions", 2008)

"In relational theory, the set of columns whose values can be used to uniquely identify each row (tuple in Dr. Codd’s original terminology) in a table (relation to Dr. Codd)." (David C Hay, "Data Model Patterns: A Metadata Map", 2010)

"The unique key (normally) used for creating foreign keys pointing to the subject table from other tables." (David C Hay, "Data Model Patterns: A Metadata Map", 2010)

"A set of one or more data attributes whose values are used to uniquely identify an entity instance or relational database table row. The primary key will have a unique value for each record or row in the table and is the means of navigation across entities and tables. Primary key attributes and values of parent entities and tables appear as foreign key attributes and values in child entities and tables." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

"The attribute, or set of attributes, that is used to uniquely identify an occurrence of the entity. Each entity must have one and only one primary key." (Craig S Mullins, "Database Administration", 2012)