Respuesta :
Alternate Key – is a column or group of columns in a table that uniquely identify every row in that table. Foreign Key – is a column that creates a relationship between two tables. The purpose of Foreign keys is to maintain data integrity and allow navigation between two different instances of an entity.
Keys are an important part of any Relational Database. There are various types of keys and among one of these is the Alternate Key. The keys that contain all the properties needed to become a Candidate Key are known as Alternate Keys. These are basically secondary Candidate Keys that can uniquely identify a row in a table. So, Alternate Keys are also sometimes known as “Secondary Keys”.
In other words, we can define the Alternate key as the set of Candidate Keys other than the Primary Key. There can be many Candidate Keys for a given table and out of all these the Database Administrators selects only one of these as the Primary Key. Hence, the other Candidate Keys which are not used as a Primary Key are the “Alternate Keys”.
Some important points about Alternate Keys are as follows :
- A Primary Key can’t be an Alternate Key. For a table with a single Candidate Key which has to be the Primary Key will not contain any Alternate Key.
- A Foreign Key can’t be an Alternate Key as it is only used to reference another table.
- The alternate Key should be unique.
- An Alternate Key can be a set of a single attribute or multiple attributes.
- It can be NULL as well.
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