Is the primary key only meant for rows or is it even for columns

Answer 1

It is for rows only. In each table, you will have at list one column that all its rows must have no duplicated value.

For example, you have a column named "student_id", and each rows in this column must be unique/non-duplicated.

Why not columns? Well, that is because each row contains different information. For example, your "mailing_address" and "billing_address" could be the same although they are different columns.

Answer 2

It is only meant for rows

Answer 3

primary key is for rows to have unique values

Answer 4

so according to you only rows have unique values is it?

Answer 5

Well, each row contains a series of information. For example, SSN, LName, FName. Those are 3 columns and you have 5 rows, for example.

Your primary key is SSN. That is, you can have 5 people under the exactly same name but with different SSN. And you are using SSN to differenciate which person you are referring to.

Answer 6

And if someone have same FName and LName, that is fine. Because they don't need to be unique.