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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.
Entity integrity is an integrity rule which states that every table must have a primary key and that the column or columns chosen to be the primary key should be unique and not null. Referential integrity concerns the concept of a foreign key. The referential integrity rule states that any foreign-key value can only be in one of two states.
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 ...
Referential integrity Values in two relational database tables can be linked through foreign key and primary key. If values in the foreign key field are not constrained by internal mechanisms, then they should be validated to ensure that the referencing table always refers to a row in the referenced table. Spelling and grammar check
Third normal form (3NF) is a database schema design approach for relational databases which uses normalizing principles to reduce the duplication of data, avoid data anomalies, ensure referential integrity, and simplify data management.
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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.