Re: renumber table

["David Spadea" <david.spadea@xxxxxxxxx>]

Steve,

I'd just like to add that I agree with Scott that this is asking for trouble if the field being renumbered is used as a foreign key somewhere. If you have no way of changing this logic, you should at least look into 'on delete cascade' and 'on update cascade' on your dependent tables. You can expect performance to suffer if the dependent tables are large, but at least you don't lose referential integrity. 

Dave

On Thu, Jun 19, 2008 at 7:07 PM, David Spadea <david.spadea@xxxxxxxxx> wrote:

Steve,

Here's your problem and its solution as I understand it:

-- Given an example table like this (data isn't too important -- just the sequencing)
create table meh
(
      id        serial primary key
    , word   varchar(10)
);

-- Populate it with data

insert into meh (word) values
    ('one'),
    ('two'),
    ('three'),
    ('four'),
    ('five'),
    ('six'),
    ('seven'),
    ('eight'),
    ('nine'),
    ('ten');

-- Delete a row from the middle of the table
delete from meh where id = 5;

-- Renumber all of the rows ABOVE the deleted row
-- This will maintain sequencing. This assumes that no gaps existed prior to the delete of this row,
-- and that only one row was deleted.

update meh
set id = id - 1
where id > 5;

At this point, if you've got a sequence that populates the id field, you'll need to set its nextval.


Dave

On Thu, Jun 19, 2008 at 7:54 AM, Steve Clark <sclark@xxxxxxxxxxxxx> wrote:

Scott Marlowe wrote:

On Wed, Jun 18, 2008 at 3:50 PM, Steve Clark <sclark@xxxxxxxxxxxxx> wrote:

I realize this is certainly not the best design - but at this point in time
it can't be changed. The table
is rarely updated and never concurrently and is very small, typically less
than 100 rows so there really is
no performance impact.

Then the easiest way to renumber a table like that is to do something like:

create temp sequence myseq;
update table set idfield=nextval('myseq');

and hit enter.
and pray.  :)

Hi Scott,

I am not sure that will do what I want. As an example
suppose I have 5 rows and the idfield is 1,2,3,4,5
now row 1 is updated, not the idfield but another column, then row 3 is deleted.
Now I would like to renumber  them such that 1 is 1, 2 is 2, 4 is 4 , 5 is 4.

I don't think what you wrote will necessarily keep them in the same relative order that they
were before.

Regards,
Steve

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