3. PRIMARY KEY
A primary key, also called a primary keyword, is a column in a relational database table that's distinctive for
each record.
It's a unique identifier, such as a driver's license number, telephone number with area code or vehicle
identification number (VIN).
A relational database must have only one primary key.
4. CANDIDATE KEY
A candidate key is a set of one or more columns that can uniquely identify a row within a table, while a
primary key is a candidate key that is chosen to be the official unique identifier for a row within the table.
A table can have multiple candidate keys, but can only have one primary key.
5. SUPER KEY
Super key is a single key or a group of multiple keys that can uniquely identify tuples in a table.
Super Key can contain multiple attributes that might not be able to identify tuples in a table independently,
but when grouped with certain keys, they can identify tuples uniquely.
6. FOREIGN KEY
A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between
the data in two tables to control the data that can be stored in the foreign key table.
7. ALTERNATE KEY
An alternate key is the secondary candidate key that contains all the property of a candidate key but is an
alternate option.
8. COMPOSITE KEY
In database design, a composite key is a candidate key that consists of two or more attributes (table columns)
that together uniquely identify an entity occurrence (table row).
