Hello 2011/1/5 Peter Eisentraut <pete...@gmx.net>: > On sön, 2011-01-02 at 12:47 +0100, Florian Pflug wrote: >> > Here's a patch to add support for negative index values in fetching >> > elements from an array. >>
negative arguments for array can be really strange >> That won't work. In SQL, array indices don't necessarily start with 0 (or 1, >> or *any* >> single value). > > FYI, this is true for PostgreSQL, but not in SQL in general. In the > standard, array indexes go from 1 to N. > >> The only way around that would be to introduce magic constants "lower", >> "upper" that >> can be used within index expressions and evaluate to the indexed dimension's >> lower >> and upper bound. You'd then use >> >> my_array[upper], my_array[upper-1], ... >> >> to refer to the last, second-to-last, ... element in the array. Actually >> doing this >> could get pretty messy, though - not sure if it's really worth the effort... > > How about just some functions: > > array_first(array, dim) > array_last(array, dim) > > Perhaps some variants for splice vs. scalar. Itakagi has a function trim_array in http://archives.postgresql.org/message-id/aanlktinrrubdsswvqo481sl0eygz830=mfkadk_kn...@mail.gmail.com patch. It's similar to array_first. I understand to a missing functionality for FIFO or LIFO queues implementation based on array. There can be function that reduce a array to first or last n items, and functions that returns first or last items. some like array_first(array, items), array_last(array, items), array_remove_first(array, items), array_remove_last(array, items) or some similar Pavel > > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers > -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
