Composite key

Composite key, also known as a compound key or concatenated key, is a type of database key that is composed of two or more fields in a database table. Such keys serve to identity records and to uniquely link the records across multiple related tables. Composite keys are commonly used in databases and databases tables to ensure that each record is unique.

A composite key can be applied to a database table in two ways. The first way is to create a single field that contains the combination of the component fields that create the key. This field is commonly referred to as an amalgamated key. Alternatively, the component fields can be used independently and are referred to as separate fields.

The composite key allows records to be linked across multiple related tables and ensures that the records contained within those tables are uniquely identified. For example, a composite key composed of two fields, such as a first name and a last name, can be used as the primary key connecting two related tables, such as those storing information about customers and their orders. That way, it is guaranteed that the customer orders in one table are linked to the same customer in the other.

Moreover, composite keys provide additional advantages such as improved querying performance due to the increased search granularity of the keys. In addition, a single composite key can be easier to deal with than multiple primary keys, thus simplifying database design.

Composite keys have some disadvantages. They are not naturally hierarchical and thus cannot be used for range queries and other types of searches. Also, composite keys require an increase in the storage space to accommodate additional fields and require extra time for design implementation.

Overall, composite keys are very useful database tools and help ensure the integrity of data retrieved from multiple related tables.