oracle - COUNT 返回 NULL，应该返回 0

Question

我对表有一个简单的查询：

Person id Organization id  employee_nam age  busines_group_id
123       Zuyo         10     John      30   81
2457      Zuyo         10     Geet      69   81
56        Ghiya        12     paul      20   81 
          frei         13                    81

SELECT
    COUNT(DISTINCT ped.person_id)
FROM
    per_emp_detail ped
WHERE
    ped.business_group_id = 81
    AND
    ped.id = NVL(p_org_id, ped.organization_id);

SELECT
    NVL(COUNT(DISTINCT ped.person_id), 0)
FROM
    per_emp_detail ped
WHERE
    ped.business_group_id = 81
    AND
    ped.id = NVL(p_org_id, ped.organization_id);

p_org_id是我传递的参数，可以是 10、12 或 13。 COUNT返回2id 10。返回1id 12。但返回NULLid 13。在这种情况下，我想0返回。

NVL并且CASE也不工作。

Answer 1

尝试最大：

nvl(max(count(DISTINCT ped.person_id)),0)