It is an excessively bad practice to have to update them ever. If there is a 0. You can also catch regular content via Connor's blog and Chris's blog. Or if video is more your thing, check out Connor's latest video and Chris's latest video from their Youtube channels. And of course, keep up to date with AskTOM via the official twitter account.
Questions Regarding On Update Cascade. Question and Answer. You Asked Dear Tom, We know that when we delete a parent record, automatically child record also will be deleted if we used "on delete cascade". Tom, I agree with your advice, but query your use of terms. A primary key that is made up via a sequence surely IS a surrogate key. The natural primary key may well be the one that has a 0. The only primary keys that could never require an update are surrogate keys, where the key value has no meaning like a sequence number.
October 07, - am UTC. A primary key is something that doesn't change. If your primary key changes, it is not a primary key -- a candidate key if you will but not a primary key.
Your right, I should have called it a "candidate key". Thanks Mr. Thank you very much Mr. Tom for your timely response. Hi Tom, I have a trigger to update child record after updating primary key of parent record. It should not work, but it works Oracle I don't know why.
January 31, - pm UTC. Well, we did that to ourselves. The database only did what it was asked to do in this case Caveat Emptor. Do NOT do this in a trigger. In fact -- beware of triggers that might depend on the order of rows being updated. Use deferrable constraints.
Perform the updates in a stored procedure. Always do it in a controlled, safe, predicable manner. Better yet -- don't do it. Cascade update will be a good feature. Dear Tom, Cascade update will be a good feature, if you can incorporate in later relaeases. Take a case like this. One fellow put customer code ' A' and 'A' for customer master.
While searching he will always find two similar customers, as code is important for him. I think you always personally disagree with a feature, that is not there in Oracle. Hi Tom, I had a discussion today with our developers regarding using Surrogate keys as primary key and one the major reason was to support Cascade Update.
They asked why Oracle doesn't support this? Why does it support Cascade Delete but not update? I couldn't answer! As always , could you please let us know?
Thanks, Arash. June 08, - pm UTC. Hence, you need to find something imutable. As always the best answer! Agreed that it is good design NOT to ever use update cascade, but Also, update cascade is sometimes needed for foreign keys whose parent keys that are not primary, but unique whose values are [albeit still rarely] mutable. February 14, - pm UTC. In reading through the past review something jumped out about you response to the trigger, highlighting the inherent problem with updating a key and it cascading causing bad data.
The problem I had is in your use of the update query. An update to a key should not be without a where condition. After all this is not a update salary kind of thing. I would also point out that over time the natural key may change from programmatic or policy changes. This would cause a new record and connecting the dots, then cleaning up the old. Or, the same effect as cascading update.
Surrogate keys by nature require the database to have additional constraints, indexes and joins that are unnessary if you use the natural key that data required to uniquely identify the non-key data.
In small applications this is irrelevant, but in large enterprise applications this can be painful. October 05, - pm UTC. Your update cascade is very usefull. I have one question. Is this restriction has been over come or its still there. Updates to primary keys that do not generate 'new' primary keys are not currently supported. For example, take the standard DEPT table.
NOTE: an update that affects a single row will never suffer from this problem. If its still there is it possible to overcome it. Thanks, Karthick. June 27, - am UTC. I pray this never becomes part of the database. Any restrictions that were there - will still be there.
I disagree about 'Primary keys are supposed to be immutable'. There is no such scientific evidence to it. Indeed, the primary keys are ok to be changed. If an id the primary key column of the table products changes, then the related description in the child tables should change too.
Think about the bar-code or serial as the id of the product This even makes more sense on temporal data. On temporal data, for example, we combine the id of the product with the start date and stop date.
The three columns become primary key. We should be able to change this, and the changes should be cascaded to the child tables. I don't know why you personally never found a use for it. I find it very useful, and the lack of declarative referential integrity for cascaded-update in Oracle troubles me.
Bernaridho www. July 09, - pm UTC. How can you have "scientific evidence" about the basic premise. Therein lies your mistake. It is not the primary key. If a bar-code or serial changes - guess what, it isn't the primary key - it just isn't. And your "temporal" example doesn't fly. If the three column become the primary key - well, no - they don't. The primary key is the ID. You have flag deleted the old data, but the primary key is still ID. Say that I don't have scientific evidence, then what is your basis for saying 'Primary keys are supposed to be immutable'?
Is your saying based on scientific evidence? If it's not and you don't say that your claim is based on scientific evidence. So you imply that we just believe you for your claim without scientific evidence? It's fallacy. What is your basis on claiming that just because the id product can change it's not a key? Again, a baseless accusation. Why they don't? You're playing God here! Why is that? Prove it to us with examples. Otherwise that is just silly, baseless opinion not worthy of thinking.
July 29, - am UTC. That is all. Do you know how to script all the foreign keys RLF? I was working on the same thing and same link see my edit RLF — mounaim. You sure can. Kris Gruttemeyer Kris Gruttemeyer 3, 1 1 gold badge 19 19 silver badges 43 43 bronze badges. Drop and recreate Sign up or log in Sign up using Google.
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