| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Derrick Rice <derrick(dot)rice(at)gmail(dot)com> |
| Cc: | pgsql-general <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Are identical subqueries in unioned statements nonrepeatable? |
| Date: | 2010-07-22 18:39:02 |
| Message-ID: | 1279823866-sup-7923@alvh.no-ip.org |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-general |
Excerpts from Derrick Rice's message of jue jul 22 12:27:31 -0400 2010:
> Is it possible for the contents of reference_table to differ from the first
> select to the select on the right hand side of the union? (e.g. because
> some other transaction committed additional rows).
No.
> If it is not possible, why? Is it because a single query always executes
> with serializable (effective) isolation?
Yes. (Actually: it's because a query is always executed with a single
snapshot).
> Is it because postgresql
> recognizes that the query is repeated and uses a single result set in both
> sides of the union?
No.
> Is this behavior that is part of postgresql intentionally, or a side effect
> that I should not rely on?
It is intentional and will not be changed.
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