From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
Cc: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Alex Ignatov <a(dot)ignatov(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Strange behavior of some volatile function like random(), nextval() |
Date: | 2016-06-29 15:04:51 |
Message-ID: | 7986.1467212691@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> A correlated subquery, on the other hand, has to be called once for every
> row and is evaluated within the context supplied by said row. Each time
> random is called it returns a new value.
> Section 4.2.11 (9.6 docs)
> https://www.postgresql.org/docs/9.6/static/sql-expressions.html#SQL-SYNTAX-SCALAR-SUBQUERIES
> Maybe this could be worded better but the first part talks about a single
> execution while "any one execution" is mentioned in reference to "the
> surrounding query".
> I do think that defining "correlated" and "non-correlated" subqueries
> within this section would be worthwhile.
Hmm ... a quick look around says we don't define or use those terms
anywhere. I agree this could stand to be addressed somewhere, but I'm
not sure if 4.2.11 is the most appropriate place. I don't think the
issue is unique to scalar subqueries.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Robert Haas | 2016-06-29 15:14:59 | Re: pgbench unable to scale beyond 100 concurrent connections |
Previous Message | Amit Khandekar | 2016-06-29 15:00:21 | Re: asynchronous and vectorized execution |