Re: Joins of data-modifying CTE with the target table

To reiterate, I (I personally) get why it's not working, but the
documentation is something that is intended for people who don't.

Technically, anyone can deduce it from reading the documentation thoroughly
enough, but do we need the documentation to be as terse as possible?

To answer your question, by "explicitly" I mean mentioning this very
pattern, where you join the returned id with the target table. People often
try to use this pattern for queries like "add an item to the order in a
CTE, select the order total in the main query", and often don't notice that
the order total doesn't include the new item until it hits production.

ср, 19 апр. 2023 г. в 11:46, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Alex Bolenok <quassnoi(at)gmail(dot)com> writes:
> > I get why it's not working (because the statement is not allowed to see
> the
> > tuples with its own cmin), but I was wondering if it was worth it at
> least
> > to spell it out explicitly in the documentation.
>
> What's not explicit about this?
>
> The sub-statements in WITH are executed concurrently with each other
> and with the main query. Therefore, when using data-modifying
> statements in WITH, the order in which the specified updates actually
> happen is unpredictable. All the statements are executed with the same
> snapshot (see Chapter 13), so they cannot “see” one another's effects
> on the target tables.
>
> regards, tom lane
>