How to resolve ORA-00937: not a single-group group function when calculating percentage?

Question

I\'m trying to get a percentage of the itemid that are available in a certain area. Using my query, I get an error ORA-00937: not a single-group group function<

Answer 1

I guess even this helps:

SELECT
    distinct areas,
    NVL(x.count_item * 100,0) AS Percentage
FROM
    allitems a
    LEFT OUTER JOIN (
        SELECT
            ( COUNT(a.itemid) / (
                SELECT
                    COUNT(*)
                FROM
                    allitems
            ) ) AS count_item,
            areas AS avl_areas
        FROM
            allitems       a
            INNER JOIN currentitems   c ON a.itemid = c.itemid
        GROUP BY
            areas
    ) x ON x.avl_areas = a.areas
;