Composite key
Composite key
Composite key definition
A composite key is a combination of two or more columns that uniquely identify a row within a database table. While each column may not be unique on its own, their combined values are guaranteed to be unique across the table.
See also: cloud database, database replication, database report
How composite keys work
In relational databases, primary keys are used to uniquely identify rows. Sometimes, no single column can serve as a primary key because its values are not unique. In these cases, a combination of columns can be used. This combination is called a composite key. When establishing relationships between tables using foreign keys, the same combination of columns must be referenced.
Advantages of using composite keys
- They often represent data relationships more naturally than single artificial keys.
- Composite keys ensure that the combination of values is unique, maintaining data integrity.
- Allows for a wider range of unique combinations than a single column.
Disadvantages of using composite keys
- Complicates queries and joins, leading to performance issues.
- The combined length of columns could exceed the system’s maximum index size.
- It requires constant maintenance because of changes in table structure or business requirements.