Relational Database Design and Modeling for Software Engineers
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Relational Integrity Constraints

A new clerk types a marks value of 210 out of 100. Another inserts a loan for a member id that does not exist. A third leaves a primary key empty.

None of these should be possible. Each one is a rule the database can enforce for you, on every application that ever connects, and each has a name.

An integrity constraint is a rule the data must always obey. The database checks it on every insert, update and delete, and refuses anything that breaks it.

Domain constraints

A domain constraint limits an attribute to a set of allowed values.

The most basic form is the data type. Declaring

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