The child record is any record with a matching PK.
If these are not selected, the system will prevent the deletion or update of PK values in the parent table (Customer table) if a child record exists. For example, the Edit Relationships window in MS Access (see Figure 9.1) shows two additional options for FK rules: Cascade Update and Cascade Delete. Listed below are the statements showing the FK in the Order table referencing the PK in the Customer table.ĬustID INTEGER REFERENCES Customer(CustID),Īdditional foreign key rules may be added when setting referential integrity, such as what to do with the child rows (in the Orders table) when the record with the PK, part of the parent (Customer), is deleted or changed (updated). When using Transact-SQL, the referential integrity is set when creating the Order t able with the FK. Referential integrity using Transact-SQL (MS SQL Server)
See Figure 9.1 for a view of how this is done on the Edit Relationships screen in MS Access. In Microsoft (MS) Access, referential integrity is set up by joining the PK in the Customer table to the CustID in the Order table. Referential integrity in Microsoft Access Relational database systems are easier to use and understand than other database systems. Codd of IBM’s San Jose Research Laboratory. RDBMS is a popular database system that is based on the relational model introduced by E. When setting up referential integrity it is important that the PK and FK have the same data types and come from the same domain, otherwise the relational database management system (RDBMS) will not allow the join. In this situation, it’s not enough that the CrsCode and Section in the Class table make up the PK, we must also enforce referential integrity. The referential integrity constraint states that CrsCode in the Class table must match a valid CrsCode in the Course table.
Recall that a typical join is between a PK and FK. To ensure that there are no orphan records, we need to enforce referential integrity. An orphan record is one whose foreign key FK value is not found in the corresponding entity – the entity where the PK is located. It means the reference from a row in one table to another table must be valid.Įxamples of referential integrity constraint in the Customer/Order database of the Company : Referential integrity requires that a foreign key must have a matching primary key or it must be null. This constraint is specified between two tables (parent and child) it maintains the correspondence between rows in these tables. For example, in the EMPLOYEE table, Phone cannot be a primary key since some people may not have a telephone. This is because null values for the primary key mean we cannot identify some rows. Neither the PK nor any part of it can contain null values. To ensure entity integrity, it is required that every table have a primary key. There are several kinds of integrity constraints, described below.
Such information is provided in logical statements called integrity constraints. For example, the Employee ID (EID) must be unique or the employee Birthdate is in the range. We need more specific ways to state what data values are or are not allowed and which format is suitable for an attribute. However, there are real-world semantics for data that cannot be specified if used only with domain constraints. Domain Integrityĭomain restricts the values of attributes in the relation and is a constraint of the relational model. Constraints are the rules that force DBMSs to check that data satisfies the semantics. Constraints are useful because they allow a designer to specify the semantics of data in the database. In fact, the relational model supports the well-defined theory of constraints on attributes or tables. Chapter 9 Integrity Rules and ConstraintsĬonstraints are a very important feature in a relational model.