Coalesce 2 Arrays

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

Yes, they are.

On Tue, Jun 25, 2019 at 4:33 AM Rob Sargent <robjsargent@gmail.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@gmail.com
<mailto:robjsargent@gmail.com>> wrote:

On Jun 24, 2019, at 2:31 PM, Alex Magnum <magnum11200@gmail.com
<mailto:magnum11200@gmail.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)

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@gmail.com
<mailto:robjsargent@gmail.com>> wrote:

On Jun 24, 2019, at 2:31 PM, Alex Magnum <magnum11200@gmail.com
<mailto:magnum11200@gmail.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)

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

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

On 6/24/19 5:19 PM, David G. Johnston wrote:

On Mon, Jun 24, 2019 at 4:11 PM Rob Sargent <robjsargent@gmail.com
<mailto:robjsargent@gmail.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@gmail.com <mailto:robjsargent@gmail.com>> wrote:

On Jun 24, 2019, at 2:31 PM, Alex Magnum
<magnum11200@gmail.com <mailto:magnum11200@gmail.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.

Brilliant of course.  Maybe not as easy to stick in another query

select a.name, b.name, tt(a.intarray, b.intarray) as coalesced_array
from table a join table b on a.<something> = b.<something>;

Any guess at the performance differences?