Re: Phantom Inserts

In article <3ikkjp$qi6@jac.zko.dec.com> feenan@nova.enet.dec.com "Jay Feenan" writes: > >In article <793588545snz@granby.demon.co.uk>, bh@granby.demon.co.uk (Bruce > Horrocks) writes... >> >>Funny how both the responses form Oracle personnel mentioned Rdb >>rather than (original) Oracle. > >Since the original posting was in the comp.databases.rdb newsgroup and we >tend to follow it closely... I didn't intend this to become a big issue, its just that the original was posted to both c.d.rdb _and_ c.d.oracle but only the Rdb people responded. [snip] >>>BTW, how important is the protection against phantom inserts anyway? >>>It doesn't seem common in applications that I have seen. >> >>I don't think that I've ever had to worry about it in any application >>that I've written. Doing the same select twice in a row in the same >>transaction would be so obviously inefficient that I would try to >>design around it as a matter of course. > >But phantom protection is in this tread has been shown >in its most primitive form...of really pairing a select and either an >insert/update or select together. When a database engine supports other >features that the industry requires such as referential integrity it becomes >much more complex [but can always be broken down to the primitives presented]. You contradict yourself: yes the example was simple but, as you say, more complex cases can still be resolved into the primitives presented. Which means that my point applies: an "unnecesary" select is still being performed. In your defence though I would say that spotting such statements is not easy but then if it were I would be out of a job. >The fact of the matter is, when a database engine supports referential, the >many applications that you have developed would have no clue of this >requirement. The bottom line is that although your statement and mind set is >true for the applications that you've developed...phantom prevention can be a >requirement for the database that you run your application against, but you >never see it. I agree absolutely: if the requirement to prevent phantoms is introduced by the database itself then the database should be responsible for preventing them. However I don't think the orignal poster had (declarative, I presume) referential integrity in mind when posing the original question. Regards, -- ------------------------------------------------------------------------------- Bruce Horrocks Hampshire, England Object Oriented programmers only need two methods - Create and Scoop-Up bh@granby.demon.co.uk -------------------------------------------------------------------------------