are in doing data modelling?
Superkey is any subset of attributes that uniquely identifies the tuples of a relation. This subset need not be minimal, that is, one can remove some attributes from it and it is still uniquely identifying. If all redundant attributes are removed you get a subset what is called primary key. A key (better: primary key) is the minimal subset of attributes that uniquely identifies the tuples of a relation, that is, you can't remove further attributes from this subset without losing the property of unique Identification. Therefore, the super superkey (like superman) is always the set of all attributes of a relation.
...If all redundant attributes are removed you get a subset what is called primary key...
I have to make an extension:
Sometimes there are more than one superkey of a relation. In such case also all redundant attributes have to be removed and the remaining subsets of attributes are then called CANDIDATE KEYS. Now one can freely select ONE of these candidate keys to identify the relation's tuples. In such case, this selected subset is called PRIMARY KEY.
Hi, I am a newbie in developing a website. i have tried to connect using mysqli conncetion
Here is my simple code.
// db.php code
//$con = mysqli_connect("localhost","root","","bakery"); ...
If you're in one of those predicaments where cls.__private attributes just aren't enough since they can easily be accessed through inst._cls__private, and you need something a little more secure, here's ...