Here are the key points about different types of keys in the relational model:
1. Candidate Key:
- It is a minimal set of attributes that can uniquely identify a tuple.
- Every table must have at least one candidate key.
- A table can have multiple candidate keys but only one primary key.
- The value of the candidate key is unique and may be null for a tuple.
2. Primary Key:
- It is a unique key that can identify only one tuple at a time.
- It cannot have duplicate or null values.
- It can be composed of more than one column.
3. Super Key:
- It is a set of attributes that can uniquely identify a tuple.
- Adding zero or more attributes to the candidate key generates the super key.
4. Alternate Key:
- It is a candidate key other than the primary key.
- All keys which are not primary keys are called alternate keys.
5. Foreign Key:
- It acts as a primary key in one table and as a secondary key in another table.
- It combines two or more relations at a time.
6. Composite Key:
- It is used when a single attribute does not uniquely identify all the records in a table.
- It is composed of multiple attributes and used together to uniquely identify rows in a table.
These types of keys are essential in database management systems as they help in distinct identification, relation development, and maintaining data integrity between tables.
