Re: Array aggregation. Was: PostgreSQL Final Release ... Monday?

Hannu Krosing <hannu(at)krosing(dot)net> writes:
> 2. Is there a way to define a function such that

> declare make_array(any) returns any[] ?

No. We do need a way to construct an array as an expression result,
but I think it will have to be a special syntactic case, not an ordinary
function. Maybe something roughly like a CAST construct,
ARRAY(expr,expr,expr,... OF type-name)

The function definition language isn't nearly powerful enough to deal
with this --- heck, we don't even support a variable number of
arguments. If it were, it'd probably break the whole ambiguous-
function-call resolution mechanism --- what type do you assign to the
output if you're not entirely sure how the inputs are to be interpreted?

> 3. Also, can I prescribe order of aggregation (aggregation applied
> _after_ ORDER BY) that would act in a way similar to HAVING .

Sub-select in FROM might help here.

> 4. what arguments must I give to array_in so that it produces an
> array of specific kind ?

You don't. array_in is meant to be used as the declared typinput
routine for an array type; that linkage is what causes the system
to know what the output array type is. array_in by itself can't
cause the system to assign a correct type to its result.

regards, tom lane