Editing Primary key (section)

{{Short description|Relational databases concept}}
{{one source|date=June 2021}}
In the [[relational model]] of [[database]]s, a '''primary key''' is a designated attribute ([[Column (database)|column]]) that can reliably identify and distinguish between each individual record in a [[Table (database)|table]]. The database creator can choose an existing unique attribute or combination of attributes from the table (a [[natural key]]) to act as its primary key, or create a new attribute containing a [[unique identifier|unique ID]] that exists solely for this purpose (a [[surrogate key]]). 

Examples of natural keys that could be suitable primary keys include data that is already by definition unique to all items in the table such as a [[national identification number]] attribute for person records, or the combination of a very precise [[timestamp]] attribute with a very precise location attribute for event records.

More formally, a primary key is a <em>specific choice</em> of a <em>minimal</em> set of attributes that uniquely specify a tuple ([[Row (database)|row]]) in a [[Relation (database)|relation]] (table).{{efn|Corresponding terms are respectively theoretical (attribute, tuple, relation) and concrete (column, row, table).}}<ref>{{cite web |url=https://support.office.com/en-us/article/add-or-change-a-table-s-primary-key-in-access-07b4a84b-0063-4d56-8b00-65f2975e4379 |title=Add or change a table's primary key in Access |publisher=Microsoft |access-date=January 20, 2020 |quote=A primary key is a field or set of fields with values that are unique throughout a table.}}</ref> A primary key is a choice{{clarify|date=August 2024}} of a [[candidate key]] (a minimal [[superkey]]); any other candidate key is an '''alternate key'''.