A value used to identify a record in a database, derived by applying some fixed function to the record. The key is often one of the fields (a column if the database is considered as a table with records being rows). Alternatively the key may be obtained by applying some function, for example, a hash function, to one or more of the fields. The set of keys for all records forms an index. Multiple indexes may be built for one database depending on how it is to be searched. See also indexed file.