# 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

**composite keycomposite primary keyCompound**

### Foreign key

**Foreignforeign key constraintforeign key references**

### 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**

### 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.

### Boyce–Codd normal form

**BCNFBoyce-Codd normal formBoyce Codd Normal Form**

### 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.