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Re: Check Constraints in Roadmap?
Posted by: David Skarjune
Date: February 15, 2006 01:53PM

Jay, thanks so much for your response, which I appreciate and which got me thinking.

Jay Pipes wrote:
> As all features in the MySQL server, you can always
> write your own implementation of check constraints

If I were a C/C++ programmer with time on my hands, that'd be interesting...
But I'm an Electronic Documents Professional (EDP) and web/db programmer...

> I believe it is still considered a nice-to-have :(

E.F. Codd Rule 10: Integrity Independence
The database language should support constraints on user input that maintain database integrity.

Of course, there are interpretations of what kind(s) of integrity is needed, from four general levels:
Entity | Domain | Referential | User-Defined

Data Types are the minimal support for Domain Integrity. In MySQL, ENUM is an attempt to handle ranges, but it's not standard and it's not a boolean expression.

> it's hard to make the case that CHECK CONSTRAINTs are a critical aspect to a database server when they can be abstracted out to the application code layer

Yes, and MySQL users used to say the same thing about Referential Integrity prior to InnoDB--Sure, anything can be abstracted out and you could go back to hacking fixed width files as a programmer...

ISO SQL (and MySQL parsing) does recognize CHECK CONSTRAINTS as a standard method for enforcing domain integrity, and it's used by all major databases. When you talk to DBAs in the field who are looking at migration issues, validation comes up, and MySQL comes up short.

My only idea at this point is to write Stored Functions with boolean expressions for validation called by triggers. That what, they'd be easy to manage for reuse and not junk up the trigger when there's complex business rules running there. It's a workaround, but one that I could implement in my work immediately.

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February 11, 2006 01:45PM
February 12, 2006 11:07AM
Re: Check Constraints in Roadmap?
February 15, 2006 01:53PM
February 15, 2006 06:16PM


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