Re: Function array_agg(array)

2014-10-11 22:28 GMT+07:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Seems dangerous as heck; certainly it would have side-effects far more
> wide-ranging than just making this particular function work.
>
> A safer answer is to split array_agg into two functions,
> array_agg(anynonarray) -> anyarray
> array_agg(anyarray) -> anyarray
>
> I rather imagine you should do that anyway, because I really doubt
> that this hack is operating quite as intended. I suspect you are
> producing arrays containing arrays as elements, not true 2-D arrays.
> That's not a direction we want to go in I think; certainly there are
> no other operations that produce such things.
>

Thanks for the review. Yes, it looks like the patch produced array as the
elements. So, all array operations behaves wierdly.

In this quick & dirty patch, I am trying to implement the
array_agg(anyarray), introducing two new functions:
- array_agg_anyarray_transfn
- array_agg_anyarray_finalfn

At first, i want to use accumArrayResult and makeMdArrayResult, but it's
complicated to work with multi-dimensional arrays with those two functions.
So i combined array_cat with those function.

Currently, it cannot handle NULL arrays:
backend> select array_agg(a) from (values(null::int[])) a(a);
1: array_agg (typeid = 1007, len = -1, typmod = -1, byval = f)
----
ERROR: cannot aggregate null arrays

Regards,
--
Ali Akbar