Re: Coalesce 2 Arrays

On Mon, Jun 24, 2019 at 4:11 PM Rob Sargent <robjsargent(at)gmail(dot)com> wrote:

>
> On 6/24/19 4:46 PM, Alex Magnum wrote:
>
> Yes, they are.
>
> On Tue, Jun 25, 2019 at 4:33 AM Rob Sargent <robjsargent(at)gmail(dot)com> wrote:
>
>>
>>
>> On Jun 24, 2019, at 2:31 PM, Alex Magnum <magnum11200(at)gmail(dot)com> wrote:
>>
>> Hi,
>> I have two arrays which I need to combine based on the individual values;
>> i could do a coalesce for each field but was wondering if there is an
>> easier way
>>
>> array_a{a, null,c, d,null,f,null} primary
>> array_b{null,2 ,null,4,5 ,6,null} secondary
>>
>> result {a, 2, c, d,5, f,null)
>>
>> Any advice would be appreciated
>>
>> Are the inputs always of fixed dimensions eg. 1 by 7?
>>
>> create or replace function tt( a1 int[], a2 int[])
> returns int[] as $$
> declare
> aret int[];
> asize int;
> begin
> select array_length(a1,1) into asize;
> for i in 1..asize loop
> aret[i] = coalesce(a1[i], a2[i]);
> end loop;
> return aret;
> end;
>
> $$ language plpgsql;
>
> select * from tt(array[3,null], array[null,4]);
> tt
> -------
> {3,4}
> (1 row)
>
Plain SQL variant:

SELECT array_agg(COALESCE(a, b))
FROM (
SELECT
unnest(ARRAY[null, 2]::int[]),
unnest(ARRAY[1,null]::int[])
) vals (a, b);

Even if they aren't the same length the above should work, I think, as
extra rows for the shorter array will contribute padded nulls.

David J.