Oracle 聚组函数及运算符对NULL操作结果

--2
SELECT Count(n)
FROM (SELECT NULL n FROM dual
UNION ALL
SELECT 12 n FROM dual
UNION ALL
SELECT 10 n FROM dual) T
--12
SELECT Max(n)
FROM (SELECT NULL n FROM dual
UNION ALL
SELECT 12 n FROM dual
UNION ALL
SELECT 10 n FROM dual) T
--10
SELECT Max(n)
FROM (SELECT NULL n FROM dual
UNION ALL
SELECT 12 n FROM dual
UNION ALL
SELECT 10 n FROM dual) T
--22
SELECT Sum(n)
FROM (SELECT NULL n FROM dual
UNION ALL
SELECT 12 n FROM dual
UNION ALL
SELECT 10 n FROM dual) T

--NULL
SELECT 1 + 2 + NULL FROM dual ;
--NULL
SELECT 1 - NULL FROM dual ;
--NULL
SELECT 1 * NULL FROM dual ;
--NULL
SELECT 1 / NULL FROM dual ;