Domain Key Constraint
Domain constraint data type constraints not null unique primary key foreign key check default mapping constraints.
Domain key constraint. The domain key normal form is achieved when every constraint on the relation is a logical consequence of the definition of keys and domains and enfor. Bedanya adalah kalau unique key ini boleh bernilai null sedangkan primary key tidak boleh bernilai null. Domain key normal form is a normal form used in database normalization which requires that the database contains no constraints other than domain constraints and key constraints.
A domain constraint specifies the permissible values for a given attribute while a key constraint specifies the attributes that uniquely identify a row in a given table. Example consider the following student table. Unique key constraint unique key ini sebenarnya mirip dengan constraint primary key yaitu sama sama bernilai unik.
Referential integrity constraint. Domain constraint domain constraint defines the domain or set of values for an attribute. Domain key normal form is the highest form of normalization.
Domain constraint data type constraints not null unique primary key foreign key check default example. It is based on constraints domain constraint. Entity integrity constraint ensures that the primary key attribute in a relation should not accept a null value.
Domain constraints are user defined data type and we can define them like this. This is because the primary key attribute value uniquely defines an entity in a relation. Domain constraints can be defined as the definition of a valid set of values for an attribute.
The value of the attribute must be available in the corresponding domain. The data type of domain includes string character integer time date currency etc. The entity integrity constraint states that primary key value can t be null.