<depstein@xxxxxxxxxxxxxxxxx> 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
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