Dyntex.net Support Centre: MySQL Reference Manual p.39

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

Chapter 1: General Information 39 In MySQL Server, you can work around the problem of ON DELETE ... not being imple- mented by adding the appropriate DELETE statement to an application when you delete records from a table that has a foreign key. In practice this is as quick (in some cases quicker) and much more portable than using foreign keys. In MySQL Server 4.0 you can use multi-table delete to delete rows from many tables with one command. See Section 6.4.6 [DELETE], page 459. In the near future we will extend the FOREIGN KEY implementation so that the information will be saved in the table specication le and may be retrieved by mysqldump and ODBC. At a later stage we will implement the foreign key constraints for applications that can't easily be coded to avoid them. Do keep in mind that foreign keys are often misused, which can cause severe problems. Even when used properly, it is not a magic solution for the referential integrity problem, although it does make things easier in some cases. Some advantages of foreign key enforcement: Assuming proper design of the relations, foreign key constraints will make it more dicult for a programmer to introduce an inconsistency into the database. Using cascading updates and deletes can simplify the client code. Properly designed foreign key rules aid in documenting relations between tables. Disadvantages: Mistakes, which are easy to make in designing key relations, can cause severe problems- for example, circular rules, or the wrong combination of cascading deletes. A properly written application will make sure internally that it is not violating refer- ential integrity constraints before proceding with a query. Thus, additional checks on the database level will only slow down performance for such an application. It is not uncommon for a DBA to make such a complex topology of relations that it becomes very dicult, and in some cases impossible, to back up or restore individual tables. 1.7.4.6 Views It is planned to implement views in MySQL Server around version 5.0. Views are mostly useful for letting users access a set of relations as one table (in read-only mode). Many SQL databases don't allow one to update any rows in a view, but you have to do the updates in the separate tables. As MySQL Server is mostly used in applications and on web systems where the application writer has full control on the database usage, most of our users haven't regarded views to be very important. (At least no one has been interested enough in this to be prepared to nance the implementation of views.) One doesn't need views in MySQL Server to restrict access to columns, as MySQL Server has a very sophisticated privilege system. See Section 4.2 [Privilege system], page 191.

MySQL Reference Manual

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