Re: Re-order columns?

David,

On Wed, Jul 29, 2020 at 11:11 PM David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> On Wednesday, July 29, 2020, David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
> wrote:
>
>> On Wednesday, July 29, 2020, Holger Jakobs <holger(at)jakobs(dot)com> wrote:
>>
>>>
>>> That columns appear to have some kind of order and show in tools with a
>>> stable order has technical reasons and is not rooted in relational theory.
>>>
>>
>> Technical reasons are real reasons. The order of columns is very real,
>> guaranteed (beware of inherits), thing in PostgreSQL whereas there is no
>> guarantee regarding row order outside of a select query order by. That
>> said I do agree that fulfilling “ocd” drives isn’t a strong use case to
>> work on the feature.
>>
>
> As for the theory, a tuple is an ordered list so the ordering of columns
> is a precise application of that definition and a relation is just a set
> (i.e., unordered) of tuples. So the claim this isn’t rooted in relational
> theory just seems wrong.
>

The issue here is to ensure that a given column always shows up at the end,
even after you added other columns. In other words, it is a kind of "ALTER
TABLE ... INSERT COLUMN AT ..." instead of "... ADD COLUMN ...". It is more
about data modeling than relational theory...