Superkey

A superkey or super-key is defined in the relational model of database organization as a set of attributes of a relation variable for which it holds that in all relations assigned to that variable, there are no two distinct tuples (rows) that have the same values for the attributes in this set.wikipedia
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Relational model

relationalrelational data modelrelationships
A superkey or super-key is defined in the relational model of database organization as a set of attributes of a relation variable for which it holds that in all relations assigned to that variable, there are no two distinct tuples (rows) that have the same values for the attributes in this set.
In practice, several useful shorthands are expected to be available, of which the most important are candidate key (really, superkey) and foreign key constraints.

Candidate key

candidatekey candidateskeys
A candidate key is a minimal set of attributes necessary to identify a tuple; this is also called a minimal superkey.

Functional dependency

functional dependenciesfunctionally dependentinspired from relational database theory
It can be defined as a set of attributes of a relation schema upon which all attributes of the schema are functionally dependent.
The latter expresses the fact that the set {StudentID, Lecture} is a superkey of the relation.

Primary key

Alternate keydefining database keykey
Informally, a primary key is "which attributes identify a record", and in simple cases are simply a single attribute: a unique id. More formally, a primary key is a choice of candidate key (a minimal superkey); any other candidate key is an alternate key.

Compound key

Database

database management systemdatabasesDBMS
A superkey or super-key is defined in the relational model of database organization as a set of attributes of a relation variable for which it holds that in all relations assigned to that variable, there are no two distinct tuples (rows) that have the same values for the attributes in this set.

Set (mathematics)

setsetsmathematical set
A superkey or super-key is defined in the relational model of database organization as a set of attributes of a relation variable for which it holds that in all relations assigned to that variable, there are no two distinct tuples (rows) that have the same values for the attributes in this set.

Tuple

tuplesn-tuple5-tuple
A superkey or super-key is defined in the relational model of database organization as a set of attributes of a relation variable for which it holds that in all relations assigned to that variable, there are no two distinct tuples (rows) that have the same values for the attributes in this set.

Relation (database)

relationrelation schemarelations
It can be defined as a set of attributes of a relation schema upon which all attributes of the schema are functionally dependent.

Relational algebra

joinJoin (relational algebra)relational logic
The set of all attributes is a trivial superkey, because in relational algebra duplicate rows are not permitted: rows are a set (no duplicates), not a multiset (duplicates allowed).

Multiset

multisetsbagbag (multiset)
The set of all attributes is a trivial superkey, because in relational algebra duplicate rows are not permitted: rows are a set (no duplicates), not a multiset (duplicates allowed).

Projection (relational algebra)

projectionprojectionsproject
If attribute set K is a superkey of relation R, then at all times it is the case that the projection of R over K has the same cardinality as R itself.

Cardinality (data modeling)

cardinalitycardinalitiescardinality constraint
If attribute set K is a superkey of relation R, then at all times it is the case that the projection of R over K has the same cardinality as R itself.

Smart number

The smart number is conceptually similar to a superkey as defined in the relational model of database organization, but, is intended to inform end users about status of accounts.

Relational database

relational database management systemRDBMSrelational databases
Because a tuple is unique, its attributes by definition constitute a superkey.

Fifth normal form

5NF
A join dependency *{A, B, … Z} on R is implied by the candidate key(s) of R if and only if each of A, B, …, Z is a superkey for R.

Fourth normal form

4NF4NF database normalization
A table is in 4NF if and only if, for every one of its non-trivial multivalued dependencies X Y, X is a superkey—that is, X is either a candidate key or a superset thereof.

Database normalization

normalizationnormalizednormal form
Now, every record is unambiguously identified by a superkey, therefore 4NF is satisfied.

Multivalued dependency

multivalued dependenciesembedded multi-valued dependencies (EMVD s)
In database normalization, fourth normal form requires that for every nontrivial multivalued dependency X Y, X is a superkey.