Array slice subscripts (was Re: [SQL] plpgsql function with more than one array argument)

Andre Holzner <Andre(dot)Holzner(at)cern(dot)ch> writes:
> Am I doing something wrong or is this a 'feature' ?

What's biting you is that the array slice operator uses the provided
lower bounds in the resultant array. For example:

regression=# select pcha from zdec_bhab;
pcha
------------------------------------
{{11,12,13},{21,22,23},{31,32,33}}
(1 row)

regression=# select array_dims(pcha) from zdec_bhab;
array_dims
------------
[1:3][1:3]
(1 row)

regression=# select pcha[2:2][1:3] from zdec_bhab;
pcha
--------------
{{21,22,23}}
(1 row)

regression=# select array_dims(pcha[2:2][1:3]) from zdec_bhab;
array_dims
------------
[2:2][1:3]
(1 row)

So your function receives an array with first index starting at 2,
which it's not expecting; its attempt to fetch element [1][1] is out
of bounds and produces a NULL.

Offhand this behavior seems like a misfeature: perhaps it'd be more
sensible for the extracted slice to always have index lower bounds
set to 1. But I'd like to see some discussion before changing it
(and I don't plan to touch it before 7.2 release, in any case ;-)).

Comments anyone?

regards, tom lane