Multiple field
A multiple field is a term from database theory . It describes individual database fields that can be assigned multiple times in a data record . The order of the field assignments is not important.
example
In a database table that contains personal data records , the language skills of the individual persons should also be recorded in a database field "Language".
Since a person can speak different languages, it is necessary that an initially indefinite number of languages can be stored in this field. This is made possible by the fact that the field is defined as multiple (multiple assignments) and can be filled with any number of different contents ( e.g. "German", "English", "French", "Spanish" ) at the same time. The individual characteristics of the field are accessed by specifying an index value. If an expression (e.g. "English" ) is deleted, the index of the subsequent field values changes; these “slide down” as it were.
Multiple fields and relational theory
The use of multiple fields contradicts the first normal form of relational theory and is therefore not supported by relational database management systems . Additional tables must be created in them to accommodate fields for which multiple values can occur. In the case of object-relational databases, this can be circumvented if necessary by the field type definitions Array and Vararray .
In practice, in relational database management systems, multiple fields are often stored in a single text field. This is particularly useful when it can be foreseen, firstly, that only a small amount of individual information will occur and, secondly, that most of the accesses to the multiple field only access the entire field, but not its individual components. See Withdrawal of the first normal form for denormalization