Is it true that a database is 2NF by default if the table only has 1 primary key?

Question

i.e. there is a table with only 1 primary key (no composite keys). Is it 2NF by default? Assume that it is already 1NF

Mallorie

Patno,PatName,appNo,time,doctor say Patno is the primary key. wouldn't this be 2NF? There are no partial key dependencies. – Mallorie

Does this answer your question? when a 1NF table has no composite candidate keys is it in 2NF? – Illiquid

Answer 1

http://en.wikipedia.org/wiki/Second_normal_form

in your example, PatNo is not a primary key since PatNo may see more than one doctor, or have more than one appNo.

Vinegarroon

maybe there's only one doctor? Your answer really doesn't help at all. – Mallorie

Answer 2

Loosely speaking, a table is in 2NF if and only if it's

• in 1NF, and
• there are no partial key dependencies.

That's not quite the same thing as saying a table that has a single-column primary key is in 2NF. A table like this

person_id  full_name       phones
--
-43        Ericka Cimini   555-222-1515
                           555-232-6100
-18        Julio Martina   555-123-4567

has a single-column primary key ("person_id"), but it isn't in 1NF. (See wikipedia for details.) And since it's not in 1NF, it can't possibly be in 2NF.

Lascivious

No, your question says, "Is [a table with a single-column primary key in] 2NF by default?" Odds are good that a lot of people will remember something about a single-column primary key, and forget the part about 1NF. – Mccauley

Answer 3

I think got it now.

In my example if there is more than 1 doctor, then doctor is also partially dependent on the patient number because the doctor has to see the correct patient. It's just confusing because doctor is also transitively dependent to patNo via appNo.

Mallorie

No, there's no partial key dependency between doctor and patient number in your example. Transitive dependencies have nothing to do with 2NF. – Mccauley

Answer 4

Maybe this late response might be helpful to others. We were taught (perhaps mistakenly) that irrelevant data also fell under 2NF. So animal(phylum, class, order, family, genus, species, greek_phoneme) would not be in 2NF because Greek phonemes have nothing to do with Animals.

Kellum