Re: Issues with generate_series using integer boundaries

On 1 Feb 2011, at 21:26, Thom Brown wrote:

> On 1 February 2011 01:05, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Thom Brown <thom@linux.com> writes:
>>> I've noticed that if I try to use generate_series to include the upper
>>> boundary of int4, it never returns:
>> 
>> I'll bet it's testing "currval > bound" without considering the
>> possibility that incrementing currval caused an overflow wraparound.
>> We fixed a similar problem years ago in plpgsql FOR-loops...
> 
> Yes, you're right.  Internally, the current value is checked against
> the finish.  If it hasn't yet passed it, the current value is
> increased by the step.  When it reaches the upper bound, since it
> hasn't yet exceeded the finish, it proceeds to increment it again,
> resulting in the iterator wrapping past the upper bound to become the
> lower bound.  This then keeps it looping from the lower bound upward,
> so the current value stays well below the end.


That could actually be used as a feature to create a repeating series. A bit more control would be useful though :P

Alban Hertroys

--
If you can't see the forest for the trees,
cut the trees and you'll see there is no forest.


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