Pick until enough

[Note] this question is cross-posted to 3 unrelated ngs. Please followup
only to 1.

Hi,

How can I do this:
select g_name from goods order by g_priority where sum(g_value) < 500

I.e., I want to orderly pick from table goods so that the total picked
value is less than a defined value.

Certainly the above sql won't work (tested under mysql). How can I do it?
Thanks!

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