Editing Record (computer science) (section)

==Key field==

A record, especially in the context of row-based storage, may include '''key''' fields that allow indexing the records of a collection. A primary key is unique throughout all stored records; only one of this key exists.<ref>{{Cite web |title=Add or change a table's primary key in Access |url=https://support.microsoft.com/en-us/office/add-or-change-a-table-s-primary-key-in-access-07b4a84b-0063-4d56-8b00-65f2975e4379?ui=en-us&rs=en-us&ad=us |access-date=2022-03-01 |website=support.microsoft.com}}</ref> In other words, no duplicate may exist for any primary key. For example, an employee file might contain employee number, name, department, and salary. The employee number will be unique in the organization and will be the primary key. Depending on the storage medium and file organization, the employee number might be ''[[Indexed file|indexed]]''—that is also stored in a separate file to make the lookup faster. The department code is not necessarily unique; it may also be indexed, in which case it would be considered a ''secondary key'', or ''alternate key''.<ref>{{Cite web |title=Alternate key - Oracle FAQ |url=http://www.orafaq.com/wiki/Alternate_key |access-date=2022-03-01 |website=www.orafaq.com}}</ref> If it is not indexed, the entire employee file would have to be scanned to produce a listing of all employees in a specific department. Keys are usually chosen in a way that minimizes the chances of multiple values being feasibly mapped to by one key. For example, the salary field would not normally be considered usable as a key since many employees will likely have the same salary.