Primary Key Change Force Foreign Key Changes_问答_开发者

I have an issue I am working with an existing SQL Server 2008 database: I need to occasionally change the primary key value for some existing records in a table. Unfortunately, there are about 30 other tables with foreign key references to this table.

What is the most elegant way to change a primary key and related foreign keys?

I am not in a situation where I can change the existing key structure, so this is not an option. Additionally, as the system is expanded, more tables will be related to this table, so maintainability is very important. I am looking for the most elegant and maintainable solution, and any help is greatly appreciated. I so far have thought about using Stored Procedures or Triggers, but I wanted some advice bef开发者_开发百科ore heading in the wrong direction.

Thanks!

When you say "I am not in a situation where I can change the existing key structure" are you able to add the ON UPDATE CASCADE option to the foreign keys? That is the easiest way to handle this situation — no programming required.

As Larry said, On Update Cascade will work, however, it can cause major problems in a production database and most dbas are not too thrilled with letting you use it. For instance, suppose you have a customer who changes his company name (and that is the PK) and there are two million related records in various tables. On UPDATE Cascade will do all the updates in one transaction which could lock up your major tables for several hours. This is one reason why it is a very bad idea to have a PK that will need to be changed. A trigger would be just as bad and if incorrectly written, it could be much worse.

If you do the changes in a stored proc you can put each part in a separate transaction, so at least you aren't locking everything up. You can also update records in batches so that if you have a million records to update in a table, you can do them in smaller batches which will will run faster and have fewer locks. The best way to do this is to create a new record in the primary table with the new PK and then move the old records to the new one in batches and then delete the old record once all related records are moved. If you do this sort of thing, it is best to have audit tables so you can easily revert the data if there is a problem since you will want to do this in multiple transactions to avoid locking the whole database. Now this is harder to maintain, you have to remember to add to the proc when you add an FK (but you would have to remember to do on UPDATE CASCADE as well). On the other hand if it breaks due to a problem with a new FK, it is an easy fix, you know right what the problems is and can easily put a change to prod relatively quickly.

There are no easy solutions to this problem because the basic problem is poor design. You'll have to look over the pros and cons of all solutions (I would throw out the trigger idea as Cascade Update will perform better and be less subject to bugs) and decide what works best in your case. Remember data integrity and performance are critical to enterprise databases and may be more important than maintainability (heresy, I know).

If you have to update your primary key regularly then something is wrong there. :)

I think the simplest way to do it is add another column and make it the primary key. This would allow you to change the values easily and also related the foreign keys. Besides, I do not understand why you cannot change the existing key structure.

But, as you pointed in the question (and Larry Lustig commented) you cannot change the existing structure. But, I am afraid if it is a column which requires frequent updates then use of triggers could affect the performance adversely. And, you also say that as the system expands, more tables will be related to this table so maintainability is very important. But, a quick fix now will only worsen the problem.