Re: Coalesce 2 Arrays

["David G. Johnston" <david.g.johnston@xxxxxxxxx>]

On Mon, Jun 24, 2019 at 4:11 PM Rob Sargent <robjsargent@xxxxxxxxx> 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@xxxxxxxxx> wrote:

On Jun 24, 2019, at 2:31 PM, Alex Magnum <magnum11200@xxxxxxxxx> 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.