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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.

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