There are a variety of keys in a relational database, including:

Alternate keys are candidate keys that exclude all primary keys.
Artificial keys are created by assigning a unique number to each occurrence or record when there aren’t any compound or standalone keys.
Compound keys are made by combining multiple elements to develop a unique identifier for a construct when there isn’t a single data element that uniquely identifies occurrences within a construct. Also known as a composite key or a concatenated key, compound keys consist of two or more attributes.
Foreign keys are groups of fields in a database record that point to a key field or a group of fields that create a key of another database record that’s usually in a different table. Often, foreign keys in one table refer to primary keys in another. As the referenced data can be linked together quite quickly, it can be critical to database normalization.
Natural keys are data elements that are stored within constructs and utilized as primary keys.
Primary keys are values that can be used to identify unique rows in a table and the attributes associated with them. For example, these can take the form of a Social Security number that’s related to a specific person. In a relational model of data, the primary key is the candidate key. It’s also the primary method used to identify a tuple in each possible relation.
Super keys are defined in the relational model as a set of attributes of a relation variable. It holds that all relations assigned to that variable don’t have any distinct tuples. They also don’t have the same values for the attributes in the set. Super keys also are defined as a set of attributes of a relational variable upon which all of the functionality depends.