IFNULL

语法说明

如果 expr1 不为 NULL，则 IFNULL() 返回 expr1；否则返回 expr2。

语法结构

> IFNULL(expr1,expr2)

示例

mysql> SELECT IFNULL(NULL,10);
+------------------+
| ifnull(null, 10) |
+------------------+
|               10 |
+------------------+
1 row in set (0.01 sec)

mysql> SELECT CAST(IFNULL(NULL, NULL) AS DECIMAL);
+-----------------------------------------+
| cast(ifnull(null, null) as decimal(38)) |
+-----------------------------------------+
|                                    NULL |
+-----------------------------------------+
1 row in set (0.01 sec)