Re: Detecting which columns a query will modify in a function called by a trigger

On 3/3/20 1:32 PM, stan wrote:
Please reply to list also.
Ccing list
> On Tue, Mar 03, 2020 at 10:48:29AM -0800, Adrian Klaver wrote:
>> On 3/3/20 9:42 AM, stan wrote:
>>> On Mon, Mar 02, 2020 at 01:44:52PM -0700, David G. Johnston wrote:
>>>> On Mon, Mar 2, 2020 at 1:28 PM stan <stanb(at)panix(dot)com> wrote:
>>>>
>>>>> Envision a table with a good many columns. This table represents the "life
>>>>> history" of a part on a project. Some of the columns need to be
>>>>> created/modified by the engineer. Some need to be created/modified by the
>>>>> purchasing agent, some of the columns need to be created by the receiving
>>>>> department, some of the columns need to be created/modified by the accounts
>>>>> payable department.
>>>>>
>>>>> Make sense?
>>>>>
>>>>
>>>> On a theory level this design is insufficiently normalized. The fact that
>>>> you are having issues and challenges working with it suggests you should
>>>> seriously consider a different design, one that exhibits better
>>>> normalization properties.
>>>>
>>>> Alternatively you might consider just removing direct access to the table
>>>> and provide views and/or functions that can use normal permission grants.
>>>> Add some check constraints to the table to describe and enforce the
>>>> inter-field relationships that are present.
>>>>
>>>
>>> Thanks for the input.
>>>
>>> I have, indeed created views that restrict the subset of columns that a
>>> particular job function needs access to to the appropriate ones, but
>>> unfortunately to the best of my knowledge, I cannot INSERT/UPDATE a table
>>> through a view.
>>>
>>> Am I suffering from a lack of knowledge here?
>>
>> Yes:
>>
>> https://www.postgresql.org/docs/12/sql-createview.html
>>
>> Updatable Views
>>
>
> OK, looking at that makes me think it is fairly limited. EG an Updatable
> view can have on one FROM clause. Thus it by definition cannot use a JOIN.
> So if I have a table with may columns, I can create a view that is a subset
> of the available columns, which might be a way to address my issue.

The link was for automatically updateable views. If you want to do
something more involved then see:

https://www.postgresql.org/docs/12/rules-views.html#RULES-VIEWS-UPDATE

>
> Thanks.
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com