There is possible more than one primary key in table

Answer 1

what is foreign key?

Answer 2

you can only have one primary key in a table. you can have as many foreign keys as possible

Answer 3

You can only have one primary key per table, but it is possible to have a composite primary key consisting of multiple fields.

Answer 4

@meshwa: a foreign key is a primary key in another table. It means that values in one table (where you have your foreign key) must also appear in another table (where this value is the primary key). So, it's just reference from one table to another.