<david.sahagian@emc.com> writes:
> In postgresql.org/docs/9.1/static/transaction-iso.html I read
> 13.2.1. Read Committed Isolation Level
> . . . two successive SELECT commands can see different data, even though they are within a single transaction . . .
> Please consider this code being executed by postgres:
> = = = = = = = = = =
> select some_int from tableX
> union all
> select another_int from tableY
> ;
> = = = = = = = = = =
> Are these two select statements considered "successive" when isolation == Read Committed ?
No, the UNION is a single command. The fact that the word "SELECT"
occurs twice within it is a SQL syntactic artifact --- it doesn't
convert it into two commands.
regards, tom lane