Since you are using except and not except all, you are not looking at
arrays with duplicates.
For this case next function what the fastest for me:
create or replace function array_except2(anyarray,anyarray) returns
anyarray as $$
select ARRAY(
(
select r.elements
from (
(select 1,unnest($1))
union all
(select 2,unnest($2))
) as r (arr, elements)
group by 1
having min(arr)=max(arr)
))
$$ language sql strict immutable;
Best regards, Vitalii Tymchyshyn
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