Re: Dynamic PL/pgSQL select query: value association propblem

Zitat von Daniel Verite <daniel@manitou-mail.org>:

>     Thiemo Kellner, NHC Barhufpflege wrote:
>
>> > Why you don't create query like
>> >
>> > EXECUTE 'SELECT xxx FROM TAB WHERE A = $1.x AND B = $1.y'  USING NEW;
>>
>> I shall try. This would be the direct way, but I doubt the placeholder
>> $1 can be a record.
>
> It could be written without refering to any individual column:
>
>  IF EXISTS (select 1 from tablename
>      where tablename.* is not distinct from NEW)
>  THEN
>    -- do something
>  END IF;

Wow, I shall see if I can apply this pattern to more.

> But since the select cannot see not-yet-committed changes from other
> sessions, such a trigger cannot reliably detect duplicates, unless
> you make sure that there are no concurrent writes to the table.

This is not trigger specific but always a problem of concurrency. If
you let two processes do SCD2 on the same table at the same time on
the same business keys, you will get a messed-up table.

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