Clever Geek Handbook

Is the primary key also a super key and a candidate key?

Is the primary key also a super key and a candidate key? Their definitions are long, but I'm wondering if this is true?

Please note that I am not asking if they are the same term. I'm just asking in one direction and not the other way around.

+3


source to share


5 answers


  • A super key is a set of one or more columns that can be used to uniquely identify a record in a table

  • Candidate Key - Can be any column or combination of columns that qualifies as a unique key in the database. There can be several candidate Keys in one table. Each Candidate Key can qualify as a Master Key. You can think of this as the "shortest" super-key or the smallest super-key

  • A primary key is a column or combination of columns that uniquely identifies a record. The first Key can only be one Candidate Key.

For a candidate key to be qualified as a primary key, it must be unique and non-zero.



So basically the primary key is just one of the candidate keys, which is the minimum super key.

+7


source


According to dry definitions:

The primary key is a super key by definition - you cannot have two rows with the same primary key.
However, the primary key is not a natural obstacle for your company, but an artificial limitation in your data store: for example, you can set a person's birthday as the primary key in your desk, and there are never two people who are born on the same day. It would be silly, but possible. In this case, the table's primary key is not the domain's superkey.



However, your primary key is not necessarily the candidate key . You can add redundant columns to your primary key.

+2


source


Various attributes that can identify any row in the database are called super keys. And the minimum super-key is called as a candidate key, that is, among the set of super-keys with a minimum number of attributes. The primary key can be any key that can uniquely identify a specific row in the database. from this stream

And entering all three keys into google gives 2,480,000 results

0


source


It depends.

Primary key is the primary key used by the table to identify between different elements. It is selected from candidate keys.

Candidate keys are all keys that MAY be the master key. All keys that are unique and can be differentiated in the table.

A super key is a primary key with additional attributes, this additional information is used to uniquely identify an instance of a set of objects.

0


source


A candidate key is the smallest subset of fields that uniquely identifies a tuple. For example, if you have a candidate key in the "user_id" and "pet_id" columns, you will never have more than one tuple with the same user_id and pet_id, and neither user_id nor pet_id individually acts as a unique identifier for the tuple.

A super key is a set of fields containing a key. Using the example above, when the combination of "user_id" and "pet_id" uniquely identifies the tuple, if we added "pet_name" (which is not a key, because we can have multiple pets named "furry") it will be a super key ... It basically looks like a candidate key without the "minimum subset of fields" constraint.

The primary key is a candidate key that you tell the database to optimize. There are probably several ways to refer to a unique tuple (ie, multiple candidate keys), but you can specify it when creating the table you will use most often.

0


source






More articles:


All Articles