newyorkvast.blogg.se - Referential integrity

#REFERENTIAL INTEGRITY HOW TO#
#REFERENTIAL INTEGRITY CODE#

The parent table in the employed-by relationship is the DEPT table. For any given referential constraint, the parent table is the table that contains the primary key and the child table is the table that contains the foreign key. Two other important RI terms are parent and child tables. The rules that accompany the RI definition are just as important as the relationship. The combination of the relationship and the rules attached to that relationship is referred to as a referential constraint. Acceptable is defined in terms of an appropriate value as housed in the corresponding primary key, or a null. The concept of RI is summarized in the following "quick and dirty" definition: RI is a guarantee that an acceptable value is always in the foreign key column. In general, a foreign key must always either contain a value within the domain of foreign key values (values currently in the primary key column), or be set to null. The set of RI rules, applied to each relationship, determines the status of foreign key columns when inserted or updated, and of dependent rows when a primary key row is deleted or updated. The combination of the primary and foreign key columns and the rules that dictate the data that can be housed in those columns is the very beginning of understanding and utilizing RI to ensure correct and useful relational databases. RI appropriately embodies the integrity and usability of a relationship by establishing rules that govern that relationship. Of course, the identification of the primary and foreign keys that constitutes a relationship between tables is a component of defining referential integrity. Many people tend to over-simplify RI stating that it is merely the identification of relationships between relational tables. Referential integrity is a method for ensuring the "correctness" of data within a DBMS.

#REFERENTIAL INTEGRITY CODE#

code efficient triggers to implement all aspects of RI.

be able to code efficient SQL data definition language (DDL) create table statements using declarative RI constraints.

be able to describe the intent of each RI rule (insert, update, delete) and its various options.

#REFERENTIAL INTEGRITY HOW TO#

know what referential integrity is and how to implement referential integrity between logically related tables.

The DDL necessary to create tables using declarative RI is discussed as is using triggers to implement complete referential integrity.Īfter reading this article the reader will: RI is examined from a conceptual level first, and then from a practical, implementation oriented viewpoint. This article analyzes the various aspects that should be considered when implementing referential integrity (RI) in a Microsoft SQL Server database environment.

Referential Integrity in Microsoft SQL Server

You can’t delete a record from a primary table if matching records exist in a related table.SQL Server Update: "Referential Integrity in Microsoft SQL Server".

You can’t change the value of a primary key in the primary table if matching records exist in the related table.

You can’t add a record to a related table unless a matching record already exists in the primary table.

Once you have established referential integrity, the following rules are set: Once You Have Established Referential Integrity

You can't have a record in a related table unless a matching record already exists in the primary table.

Both tables must be in the same Access database.

The related fields must be the same data type and size.

One of the linked fields must be a primary key.

You can only use referential integrity when all the following conditions are met: Conditions for Enforcing Referential IntegrityĪccess is very picky about when you can set referential integrity. Referential integrity keeps data accurate and ensures that you don’t accidentally change or delete related data in one table but not in the other.

When you create a relationship between two tables, it is usually a good idea to enforce referential integrity.