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

1. > IFNULL(expr1,expr2)

示例

1. mysql> SELECT IFNULL(NULL,10);
2. +------------------+
3. | ifnull(null, 10) |
4. +------------------+
5. |               10 |
6. +------------------+
7. 1 row in set (0.01 sec)

1. mysql> SELECT CAST(IFNULL(NULL, NULL) AS DECIMAL);
2. +-----------------------------------------+
3. | cast(ifnull(null, null) as decimal(38)) |
4. +-----------------------------------------+
5. |                                    NULL |
6. +-----------------------------------------+
7. 1 row in set (0.01 sec)