淺談mysql可有類似oracle的nvl的函數(shù)

    要用ifnull，而不是isnull
    isnull是判斷是否為null，返回值是1表示null或者0表示不為空
    ifnull等同于oracle的nvl,用法如下
    mysql> select ifnull(1,10);
    +--------------+
    | ifnull(1,10) |
    +--------------+
    | 1 |
    +--------------+
    1 row in set (0.00 sec)
    mysql> select ifnull(null,10);
    +-----------------+
    | ifnull(null,10) |
    +-----------------+
    | 10 |
    +-----------------+
    1 row in set (0.00 sec)
    isnull的用法如下
    mysql> select isnull(null);
    +--------------+
    | isnull(null) |
    +--------------+
    | 1 |
    +--------------+
    1 row in set (0.00 sec)
    mysql> select isnull(1);
    +-----------+
    | isnull(1) |
    +-----------+
    | 0 |
    +-----------+
    1 row in set (0.00 sec)