S a subset of A, is a super key if S -> A.
That is, the combination of all attributes in S, determines all attributes in A.
Example:
R(studentNo, firstName, lastName, course, instructor)
FDs:
studentNo -> firstName, lastName, course
course -> instructor
Is studentNo a super key?
Yes, because studentNo yields the attributes firstName, lastName and course and course yield instructor. So with studentNo as super key, we are able to retrieve all the other attributes in relation R.
Is course a super key?
No, because we can only retrieve the instructor attribute and nothing else.
no they did not
why there is no answer yet
Primary Key is a Constraint Used to avoid Duplicate entries in database table and you define primary key the column doesn't allow NULL values.
A primary key is a unique identifier for a record in a database table, ensuring that each entry is distinct and can be accurately referenced. It prevents duplicate records and enforces data integrity by establishing a reliable way to access and manipulate data. Additionally, a primary key can facilitate relationships between different tables in a relational database.
In a relational database it is used as a way to uniquely identify a record in a table. It also allows tables within the database to reference the specific record within the table. For example, a common practice is to have the database automatically determine the Primary Key with an auto-incrementing value starting at 1 upon inserting each new record. The reason for uniquely identifying the record is there could be cases where the data between two records are exactly the same, but they need to be separate as they do represent different things. For example, let's say you have a database containing the name of a person "John Smith". What would happen if you added "John Smith" into the database multiple times without a Primary Key? By providing the Primary Key as shown below, you can now reference the correct "John Smith". Id Name 1 John Smith 2 John Smith
the super key is the windows key (the flag) in non-windows OS
A Super key and composite key are similar to one another. Both of them are used to uniquely identify a row in a database table. A super key is a set of columns within a table that can be used to identify a particular row in a table. A super key can be only one column or a combination of multiple columns. If a super key contains multiple columns it becomes a composite key.
super key foreign key candidate key surrogate key unique key alternate key composite key compound key
its a unique key use to identify data in database
a key is important in a database because using of that key only we can identify a unique attribute.
Different set of attributes which are able to identify any row in the database is known as super key. And minimal super key is termed as candidate key i.e. among set of super keys one with minimum number of attributes. Primary key could be any key which is able to identify a specific row in database in a unique manner.
i key field is a field with with a key in the middle :)
database
There are six keys in database that we use . Each key serves specific functions like primary is used to identify a tuple uniquely. Keys in database are Primary, surrogate, foreign, alternate , candidate, super.
There are many keys in database each having particular use. Types of keys in database are : Primary key, candidate key, alternate key, foreign key, surrogate key.
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keyboard hehehe