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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 ...
A check constraint is a type of integrity constraint in SQL which specifies a requirement that must be met by each row in a database table. The constraint must be a predicate . It can refer to a single column, or multiple columns of the table.
Examples of these include the geographic information system (GIS) data types from the PostGIS project for PostgreSQL. There is also a data type called a domain, which is the same as any other data type but with optional constraints defined by the creator of that domain. This means any data entered into a column using the domain will have to ...
This convention is technically a constraint but it is neither a domain constraint nor a key constraint; therefore we cannot rely on domain constraints and key constraints to keep the data integrity. In other words – nothing prevents us from putting, for example, "Thick" for a book with only 50 pages – and this makes the table violate DKNF.
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]
Here ID serves as the primary key in the table 'Author', but also as AuthorID serves as a Foreign Key in the table 'Book'. The Foreign Key serves as the link, and therefore the connection, between the two related tables in this sample database. In a relational database, a candidate key uniquely identifies each row of data values in a database ...
The article talks about the foreign key referencing a Candidate key in the referenced table. I dont think that this is entirely accurate. The foreign key must reference a Superkey, but there is no requirement for that Superkey to also be a Candidate key. Candidate key is a smallest possible superkey, and I'm pretty sure a foreign key can ...
a double line indicates a participation constraint, totality, or surjectivity: all entities in the entity set must participate in at least one relationship in the relationship set; an arrow from an entity set to a relationship set indicates a key constraint , i.e. injectivity : each entity of the entity set can participate in at most one ...