浅谈mysql可有类似oracle的nvl的函数的详情

要用ifnull，而不是isnull

isnull是判断是否为null，返回值是1表示null或者0表示不为空

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)

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