Given two arrays how to get items that are not in both? - sql

Question

I have two arrays in postgresql:
CREATE OR REPLACE FUNCTION func()
RETURNS void AS
$BODY$
declare
first integer[];
second integer[];
array_vb integer[];
array_vb2 integer[];
begin
code....
select array_agg(id) into first
from a
where id = any (array_vb);
select array_agg(id) into second
from a
where id = any (array_vb2);
end;
$BODY$
LANGUAGE plpgsql VOLATILE
I would like to add a raise notice that will print all items that are in first but not in second
for example:
first = [1,10,15,3,7]
second = [1,3,15,4]
it will print 10,7
How do I do that?

Answer 1

You can use PostgreSQL unsent function:
SELECT ARRAY(SELECT unnest(first) EXCEPT SELECT unnest(second))
Example:
SELECT ARRAY(SELECT unnest(ARRAY[1,10,15,3,7]) EXCEPT SELECT unnest(array[1,3,15,4]))
Gives:
array
--------
{10,7}
See SQLFiddle here.

Answer 2

You can use intarray extension:
create extension if not exists intarray;
select array[1,10,15,3,7] - array[1,3,15,4] as result;
result
--------
{7,10}
(1 row)

Answer 3

create or replace function f(a1 int[], a2 int[])
returns void as $body$
begin
raise notice '%', (
select string_agg(i::text, ',')
from
unnest (a1) a1(i)
left join
unnest (a2) a2(i) using (i)
where a2.i is null
);
end;
$body$ language plpgsql volatile
;
select f(array [1,10,15,3,7], array [1,3,15,4]);
NOTICE: 10,7
f
---
(1 row)
Notice that the above function, as it is, can be marked immutable

Answer 4

You can create a function that returns the desired array result:
create or replace function array_except(a1 int[], a2 int[])
returns int[]
as
$$
select array_agg(i)
from (
select i
from unnest(a1) i
except
select a2
from unnest(a2) a2
) t;
$$
language sql;
The function returns an array that contains the elements that are in the first, but not in the second array.
You can use the above function in your actual function:
create or replace function foo()
returns void
as
$BODY$
declare
_first integer[];
_second integer[];
begin
_first := array[1,10,15,3,7];
_second := array[1,3,15,4];
raise notice 'Result %', array_except(_first, _second);
end;
$BODY$
LANGUAGE plpgsql;