what is primary and foreign key?

Answer 1

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.