what is primary and foreign key?

Answer 1

A primary key is a unique identifier for a column in a table can not be null and does not allow repeated values in that column.

A foreign key is a reference to a key in another table, establishes the relationship between two tables.

For example, we have these two tables:
person (id, name, surname, age);
id is a primary key.
car (registration, make, model, id_person);
id_person is a foreign key, refers to the id key car owner.

I hope it helps you.

Answer 2

PRIMARY KEY -

1)it's unique . this helps in joining two different tables in a database so that no redundant data is obtained. Basically the whole column is supposed to have distinct/unique data

2) It cannot contain the null values

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FOREIGN KEY-

1)It's used as reference of Primary key. That is when you create a join in order to match data you need a corresponding foreign key.It can contain any number of duplications.

2)It can contain the null values.