Entity integrity is concerned with ensuring that each row of a table has a unique and non-null primary key value; this is the same as saying that each row in a table represents a single instance of the entity type modelled by the table. A requirement of E. F. Codd in his seminal paper is that a primary key of an entity, or any part of it, can never take a null value.
The relational model states that every
relation (or
table
Table may refer to:
* Table (furniture), a piece of furniture with a flat surface and one or more legs
* Table (landform), a flat area of land
* Table (information), a data arrangement with rows and columns
* Table (database), how the table data ...
) must have an identifier, called the
primary key (abbreviated PK), in such a way that every
row
Row or ROW may refer to:
Exercise
*Rowing, or a form of aquatic movement using oars
*Row (weight-lifting), a form of weight-lifting exercise
Math
*Row vector, a 1 × ''n'' matrix in linear algebra.
*Row (database), a single, implicitly structured ...
of the same relation be identifiable by its content, that is, by a unique and minimal value. The PK is a not empty set of
attributes
Attribute may refer to:
* Attribute (philosophy), an extrinsic property of an object
* Attribute (research), a characteristic of an object
* Grammatical modifier, in natural languages
* Attribute (computing), a specification that defines a prope ...
(or
columns). The same format applies to the
foreign key (abbreviated FK) because each FK matches a preexistent PK. Each of attributes being part of a PK (or of a FK) must have data values (such as numbers, letters or typographic symbols) but not
data marks
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. ...
(also known as
NULL marks
In SQL, null or NULL is a special marker used to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL null serves to fulfil the requirement that all ''true ...
in
SQL world).
Morphologically, a
composite primary key is in a "steady state": If it is reduced, PK will lose its property of identifying every row of its relation but if it is extended, PK will be redundant.
See also
*
Domain integrity
Data integrity is the maintenance of, and the assurance of, data accuracy and consistency over its entire life-cycle and is a critical aspect to the design, implementation, and usage of any system that stores, processes, or retrieves data. The ter ...
*
Referential integrity
Referential integrity is a property of data stating that all its references are valid. In the context of relational databases, it requires that if a value of one attribute (column) of a relation (table) references a value of another attribute (e ...
*
Null (SQL)
In SQL, null or NULL is a special marker used to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL null serves to fulfil the requirement that all ''true ...
References
Data modeling
Data quality
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