Re: Read Committed Transaction Isolation and SELECT ... UNION ... SELECT - Mailing list pgsql-general

Eric Ridge <eebbrr@gmail.com> writes:
> http://www.postgresql.org/docs/8.4/static/transaction-iso.html says:

> "Also note that two successive SELECT commands can see different data,
> even though they are within a single transaction, if other
> transactions commit changes during execution of the first SELECT."

> I get that what that means in normal cases, but what about a single
> query comprised of one or more unions:

>       SELECT ... FROM foo WHERE ...
>             UNION
>       SELECT  ... FROM foo WHERE ...

That's just one SELECT command.  Sub-SELECTs inside a query don't
count as separate commands for this purpose; the use of SELECT in
that way is just an artifact of the SQL grammar.

            regards, tom lane