What is meant by candidate key in SQL?
A candidate key is a set of attributes (or attribute) that uniquely identify the tuples in relation or table. As we know, the primary key is a minimal super key, so there is one and only one primary key in any relation, but more than one candidate key can take place.
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What is candidate key with example?
Candidate key: The minimum set of attributes that can uniquely identify a tuple is known as the candidate key. For example, STUD_NO in the STUDENT relationship. The candidate key value is unique and not null for each tuple. There can be more than one candidate key in a relation.
What are candidate keys used for?
A candidate key is a specific type of field in a relational database that can identify each unique record independently of any other data. Experts describe a candidate key that “has no redundant attributes” and is a “minimum representation of a tuple” in a relational database table.
How do I create a candidate key in SQL Server?
Declare a column as a candidate key using the UNIQUE keyword. Prefix the UNIQUE keyword with the NOT NULL specification. Like a primary key, a candidate key also uniquely identifies a row in a table. Note that a table can only have one primary key, but can have any number of candidate keys.
How do I find my candidate key?
- The first step in the process of finding a normal form and decomposing a relationship is finding the candidate. keys.
- R = (ABCDE), F = {A -> C, E -> D, B -> C}
- R = ABCDE, F = {A -> BE, C -> BE, B -> D}
- R = ABCDEF, F = {A -> B, B -> D, C -> D, E -> F}
- R = ABCD, F={AB -> C, BC -> D, CD -> A}
- R = ABCD, F={A -> BCD, C -> A}
What is the difference between primary key and candidate key?
The primary key is a unique, non-null key that uniquely identifies a record in the table. A table can only have one primary key. Candidate key is also a unique key to uniquely identify a record in a table, but a table can have multiple candidate keys.
Are candidate keys unique?
The candidate key is a single key or a group of multiple keys that uniquely identify rows in a table. A candidate key is a subset of super keys and lacks unnecessary attributes that are not important for uniquely identifying tuples. The value of the Candidate key is unique and not null for all tuples.
What is the difference between primary key and candidate key?
How do I find my superkey candidate key?
The candidate key is a superkey whose non-proper subset is a superkey, that is, suppose that if ABC is a candidate key, then neither A, B, C nor any of their combinations can be a superkey, so we can say that the candidate key is a minimal set. of attributes of an R (Relational Schema) that can be used to uniquely identify a tuple of a table.
Is the primary key a candidate key?
The primary key is a candidate key chosen to uniquely identify the tuples in the table. Primary key values must be unique and not null. There can be multiple super keys and candidate keys in a table, but there can be only one primary key in a table.
Do primary keys have to be unique?
Primary keys must contain UNIQUE values and cannot contain NULL values. A table can only have ONE primary key; and in the table, this primary key can consist of one or more columns (fields).
Can the candidate key be duplicated?
Each table can have one or more candidate keys. One of these candidate keys is selected as the primary key of the table. I also know that in order for a primary key to be selected from the candidate keys, there are conditions that must be met: there must be no null or duplicate values.