While thinking about the function behavior if its input is NULL array (e.g: NULL:int[]), i've found: - currentpatch doesn't handle empty array correctly: - when there is only one array to aggregate, the resulting array is wrong - when the first array is empty array, and the second array is also empty array, it segfaulted
- if we see NULL array as NULL values, the resulting array cannot be differentiated from array of null ints:
- SELECT array_agg(NULL::int[]) FROM generate_series(1,2); ---> {NULL, NULL} with type int[]
- SELECT array_agg(NULL::int) FROM generate_series(1,2); --> {NULL, NULL} with type int[]
> array_lower raise exception if array is empty (there are no dimensions > to inquire about) > array_upper raise exception if array is empty (there are no dimensions > to inquire about)
Well, these beg the question: is an empty array zero-dimensional, or is it a one-dimensional array of no elements, or perhaps both of those as well as higher-dimensional cases where any axis has zero elements, or ???
It's really all kind of messy ... we need to trade off simplicity of definition, ease of use, backwards compatibility, and standards compliance (though the standard has only 1-D arrays so it's of just limited help here).
So, is there any idea how we will handle NULL and empty array in array_agg(anyarray)? I propose we just reject those input because the output will make no sense:
- array_agg(NULL::int[]) --> the result will be indistinguished from array_agg of NULL ints.
- array_agg('{}'::int[]) --> how we determine the dimension of the result? is it 0? Or the result will be just an empty array {} ?
