I answered A primary key is used to ensure data in the specific column is unique. A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. Only one primary key is allowed in a table. Whereas more than one foreign key are allowed in a table. It is a combination of UNIQUE and Not Null constraints. It can contain duplicate values and a table in a relational database. Its value cannot be deleted from the parent table. Its value can be deleted from the child table. It does not allow NULL values. It can also contain NULL values.