The main key of the associated table is the foreign key. As a result, you can't have a primary key and a foreign key in the same column.
To ensure that data in a single column is unique, a primary key is employed. A foreign key is a column or set of columns in a relational database table that connects data from two other tables. It is used to identify a specific record in a relational database table.
The main key in the other table is referred to as the Reference Key. Foreign Key, on the other hand, is how you connect the second table to the primary tables (or Reference Key).
A composite key is a Candidate key that has many attributes. A foreign key is an attribute that is a primary key in its parent table but is not used in the host table. Non-unique and null values may be accepted by foreign keys.
A primary key is a field (or combination of fields) in a table that has values that are unique. Because each record has a separate value for the key, values of the key can be used to refer to whole records. Only one primary key per table is allowed.