Postgres - Function to return the intersection of 2 ARRAYs?

Question

In postgresql, you can use the && operator to return t (true) if two arrays have common members, i.e. they overlap. Is there a function/operator that will return what those common members are?

i.e. something like this

select arrray_intersection(ARRAY[1, 4, 2], ARRAY[2, 3]);
ARRAY[2]

Answer 1

Try & instead of &&

See PostgreSQL Docs for more.

Answer 2

SELECT  ARRAY
        (
        SELECT  a1[s]
        FROM    generate_series(array_lower(a1, 1), array_upper(a1, 1)) s
        INTERSECT
        SELECT  a2[s]
        FROM    generate_series(array_lower(a2, 1), array_upper(a2, 1)) s
        )
FROM    (
        SELECT  array['two', 'four', 'six'] AS a1, array['four', 'six', 'eight'] AS a2
        ) q

Works on non-integer arrays too.

Answer 3

You can use this function:

CREATE OR REPLACE FUNCTION intersection(anyarray, anyarray) RETURNS anyarray as $$
SELECT ARRAY(
    SELECT $1[i]
    FROM generate_series( array_lower($1, 1), array_upper($1, 1) ) i
    WHERE ARRAY[$1[i]] && $2
);
$$ language sql;

It should work with any kind of array, and you can use it like this:

SELECT intersection('{4,2,6}'::INT4[], '{2,3,4}'::INT4[]);