Re: nextval skips values between consecutive calls

> -----Original Message-----
> From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> Sent: Friday, October 28, 2011 7:22 PM
> To: Dmitry Epstein
> Cc: pgsql-general(at)postgresql(dot)org; Peter Gagarinov
> Subject: Re: [GENERAL] nextval skips values between consecutive calls
>
> <depstein(at)alliedtesting(dot)com> writes:
> > -- This is rather surprising
> > select nextval(' test_sequence'), generate_series(1, 1); -- 3, 1
> > select nextval(' test_sequence'), generate_series(1, 1); -- 5, 1
>
> > Is there any explanation for why nextval skips a value in the second case?
>
> The targetlist is evaluated twice because of the presence of the set-returning
> function. On the second pass, generate_series reports that it's done, and so
> evaluation stops ... but nextval() was already called a second time.
>
> SRFs in SELECT targetlists are a pretty dangerous thing, with a lot of surprising
> behaviors, especially if you combine them with other volatile functions. I
> recommend avoiding them. They'll probably be deprecated altogether as
> soon as we have LATERAL.
>
> regards, tom lane

What's a good alternative in the meantime? Suppose I need to incorporate some unnests into my select, for example? (Well, I already found one alternative that seems to work, but I am not sure that's optimal.)

Dmitry Epstein | Developer

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