Re: delta relations in AFTER triggers

Marti Raudsepp <marti@juffo.org> wrote:
> On Wed, Sep 3, 2014 at 10:49 PM, Kevin Grittner <kgrittn@ymail.com> wrote:
>> Marti Raudsepp <marti@juffo.org> wrote:
>>> The concept of "lightweight relations" that pop into existence when a
>>> certain kind of trigger definition is used somewhere in the function
>>> stack, without a CREATE TABLE, without being discoverable in
>>> information_schema etc., I find needs some more justification than
>>> I've seen in this thread. So far I've only heard that it's more
>>> convenient to implement in the current PostgreSQL code base.
>>
>> It is required by the SQL standard.
>
> I had a cursory read of the SQL 20nn draft and I don't get this
> impression. The only place I could find discussing the behavior of
> "transition tables" is in Foundation "4.39.1 General description of
> triggers", which says:
>
> "Special variables make the data in the transition table(s) available
> to the triggered action. For a statement-level
> trigger the variable is one whose value is a transition table."
>
> There is no information about the scoping of such variables, so I
> assume it refers to a regular locally scoped variable.
>
> Did I miss something?

Apparently.  I did a search on the document and counted and got 101
occurrences of "transition table".  I might be off by a few, but
that should be pretty close.  Perhaps this, from 4.14 most directly
answers your point:

| A transient table is a named table that may come into existence
| implicitly during the evaluation of a <query expression> or the
| execution of a trigger. A transient table is identified by a 
| <query name> if it arises during the evaluation of a <query 
| expression>, or by a <transition table name> if it arises during 
| the execution of a trigger. Such tables exist only for the 
| duration of the executing SQL-statement containing the <query 
| expression> or for the duration of the executing trigger.

> Are you reading a different version of the spec?

I'm looking at a draft of 200x from  2006-02-01.

--
Kevin Grittner
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