Re: i have table - Mailing list pgsql-sql

On 10/4/06 12:20 PM, "Aaron Bono" <postgresql@aranya.com> wrote:

> On 10/4/06, Erik Jones <erik@myemma.com> wrote:
>>
>> Aaron Bono wrote:
>>> On 10/4/06, *Erik Jones* <erik@myemma.com <mailto:erik@myemma.com>>
>>> wrote:
>>>
>>>     There is one non-SQL related reason that I like to be able to order
>>>     columns, at least the way they are displayed whenever the table is
>>>     described:  human comprehension.  For example, I like to group all
>>>     keys
>>>     in a table before data, that includes primary as well as foreign
>>>     keys.
>>>     So, say I'm building on to an existing application and I need to do
>> an
>>>     ALTER TABLE on an existing table to add a foreign key to an existing
>>>     table.  I'd like that key to be listed with the other keys, but
>>>     presently that's not possible in a simple way and, to be honest, I
>>>     usually just go without as the process you've described below is too
>>>     prone to user (human) error when dealing with live, sensitive data
>> for
>>>     me to want to mess with it.
>>>
>>>
>>> Ah, but it is possible... if you use views.
>>>
>>> I recommend you build views and query off them.  Then you can control
>>> the order the columns will appear.
>> Which would be great if I didn't have (many) thousands of lines of code
>> that already use the tables.  Besides, this is no where near a 'make or
>> break' thing.  It's just a matter of aesthetic preference.

Ah, but it *is* a "make or break thing."  I have seen more than one
application crash because some developer didn't understand that columns in a
relation (table) have no defined order.

This (along with its sister axiom that rows have no defined order) is one of
the most commonly misunderstood aspects of relational databases.

>
>
>
> So do it as needed and convert your application slowly.
>
> I just name my views as table_name_vw so all you have to do is modify your
> queries to hit the _vw instead of just the table.  That shouldn't take much
> time to refactor.

I wasn't condoning using select * in your application - if an application is riddled with that, it is time to start fixing the problem because it WILL bite you eventually.  I never let my team put select * in any queries that end up in the application code - bad stuff that!

Of course sometimes, especially when you are doing quick throw away queries, select * is nice and controlling the order is handy.  It is also beneficial when using a generic database tool which will almost definitely do a select *.