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A multivalued field (MVF) allows for the storage of more than one value in a database field. MVFs are somewhat controversial, with many arguing that they violate one of the very sacred tenets of database design as laid out by E.F. Codd – that “each and every datum (atomic value) in a relational data base is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.” The argument goes further than simply being academic because although MVFs certainly hold the potential to ease the creation of many-to-many relationships, they also hold the destructive ability to mess up the results of SQL queries and return false results.
A multivalued field may also be known as a multivalued dependency.
Techopedia Explains Multivalued Field
The most well-known use of MVF was in Microsoft Access 2007. This is because Microsoft wanted to make sure that Access was as compatible as possible with another closely related Microsoft product – Sharepoint. Sharepoint is now widely used for hosting intranets, and a major part of this involves working with lists. For example, a corporate intranet may involve assigning a project’s tasks to only a select group of people involved in the project. For each task, you need the ability to choose a different assignee, but still restrict all assignees to only the names on the list. It is thus beneficial to have all the list members stored in one location as a single value, rather than the more complex way of holding the data separately in another table.
Some other database engines like Oracle also support MVFs. Strangely enough, as of 2011 Microsoft’s own SQL Server does not yet support MVF.
