Search results
Results from the WOW.Com Content Network
A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
It relates the two keys. Foreign keys need not have unique values in the referencing relation. A foreign key can be used to cross-reference tables, and it effectively uses the values of attributes in the referenced relation to restrict the domain of one or more attributes in the referencing relation. The concept is described formally as: "For ...
A surrogate key (or synthetic key, pseudokey, entity identifier, factless key, or technical key [citation needed]) in a database is a unique identifier for either an entity in the modeled world or an object in the database. The surrogate key is not derived from application data, unlike a natural (or business) key. [1]
For referential integrity to hold in a relational database, any column in a base table that is declared a foreign key can only contain either null values or values from a parent table's primary key or a candidate key. [2] In other words, when a foreign key value is used it must reference a valid, existing primary key in the parent table. For ...
The foreign key is typically a primary key of an entity it is related to. The foreign key is an attribute of the identifying (or owner , parent , or dominant ) entity set . Each element in the weak entity set must have a relationship with exactly one element in the owner entity set, [ 1 ] and therefore, the relationship cannot be a many-to-many ...
The fact table also contains foreign keys from the dimension tables, where time series (e.g. dates) and other dimensions (e.g. store location, salesperson, product) are stored. All foreign keys between fact and dimension tables should be surrogate keys, not reused keys from operational data.
A candidate key is a unique identifier enforcing that no tuple will be duplicated; this would make the relation into something else, namely a bag, by violating the basic definition of a set. Both foreign keys and superkeys (that includes candidate keys) can be composite, that is, can be composed of several attributes.
In the relational model of databases, a primary key is a designated attribute that can reliably identify and distinguish between each individual record in a table.The database creator can choose an existing unique attribute or combination of attributes from the table (a natural key) to act as its primary key, or create a new attribute containing a unique ID that exists solely for this purpose ...