In databases, a "key" is a field (or a set of fields) that is used to uniquely identify data. Each key serves a specific purpose and follows certain rules:
- Uniqueness: A candidate key must be unique for each row.
- Minimality: It cannot have NULL values.
This is a selected candidate key used to uniquely identify each row in the table. The primary key must be unique and cannot contain NULL values. Additionally, the primary key is commonly used as an index to speed up data retrieval.
These are candidate keys that have not been selected as the primary key. They can be used as the primary key if needed.
A super key is a key that can be composed of one or more fields, which can uniquely identify a row in the table. The super key can be a candidate key and can include additional fields.
This is a field (or set of fields) in one table that is used to reference rows in another table. The foreign key is connected to the primary key of the table it references. This forms a relationship between two tables and helps ensure data integrity.
These keys play an important role in database design and management and are essential for the accuracy and organization of data.