The problem here is that you've defined in business logic a relationship between the records in your table, then *not defined that relationship in the database*. Now you're complaining that the database doesn't do what you want. How can it? You're not telling it everything. Remember, in a relational database: 1. A relation (or table) is a collection of items with the same properties. 2. The items are not related to each other directly. This is why order is not important. Relations (tables) are unordered sets, not ordered lists. Here's the fundamental point: records in a table are, by default, not related to each other! What determines the ordering sequence here? I have to think it's based on time? It can't be arbitrary, because SERIAL is an arbitrary sequence. If you weren't designing a database, how would you be assigning and reassigning numbers? You need a field in each record that *knows* this assigning order. The database needs to know how to figure out what the order is, since the actual number you assign to it is exactly related to that order and only that order. All we know at the moment is that you need a field "ordinal" such that for every record k, ordinal(k) = ordinal(k-1)+1 (and with some fixed value for ordinal(0)). What determines the relationship between k and k-1? Why is k-1 not k-2 or k+4? Once you do this you simply need to re-sequence this ordinal field on In/Up/De. You can probably even construct a rather elaborate VIEW to automatically calculate the ordinals declaratively, or use a separate table to track the parent-child relationship of each object and use that for numbering. Brandon Aiken -----Original Message----- From: pgsql-general-owner@xxxxxxxxxxxxxx [mailto:pgsql-general-owner@xxxxxxxxxxxxxx] On Behalf Of Bob Pawley Sent: Monday, December 04, 2006 10:40 PM To: Berend Tober Cc: pgsql general Subject: Re: [GENERAL] PG Admin I am talking about designing the control system. No one makes a perfect design at first go. Devices are deleted and others added. Until the end of the design stage the numbers need to be sequential with no gaps. After the design the numbers of each device are static and new devices are added to the sequence or fill in for abandoned devices - but that is another, separate problem. But that is beside the point. What I am looking for is a gapless sequence generator which has the ability to justify for deletions as well as additions. What I am looking for is a very simple adaptation of the serial function. All that I need it to do is to justify for design changes and not care that if it is reassinged to a different device. The fact that a particular device may, by happenstance, change it's assigned number - once twice or multiple times, during the design stage, is of no consequence - as long as the totallity of numbers assigned are sequential and gapless. Bob ----- Original Message ----- From: "Berend Tober" <btober@xxxxxxxxxxxxxxxx> To: "Bob Pawley" <rjpawley@xxxxxxx> Cc: "pgsql general" <pgsql-general@xxxxxxxxxxxxxx> Sent: Monday, December 04, 2006 7:15 PM Subject: Re: [GENERAL] PG Admin > Bob Pawley wrote: >> Your missing the point. >> >> I am creating a design system for industrial control. >> >> The control devices need to be numbered. The numbers need to be >> sequential. If the user deletes a device the numbers need to regenerate >> to again become sequential and gapless. > Could you explain what it is about industrial control that requires the > reassignment of numbers? Seems to me to make for confusion because over > time, you then have a particular instrument referred to by different > identifiers. So if you had other data, such as written logs, shop floor > design diagrams, or other data not included in the data base, for example, > you'ld have the problem of keeping track of which instruments were really > being talked about because the names (identifying number, that is) keep > changing. > > ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
