ifnull
description
Syntax
ifnull(expr1, expr2)
如果 expr1 的值不为 NULL 则返回 expr1，否则返回 expr2
example
mysql> select ifnull(1,0);
+--------------+
| ifnull(1, 0) |
+--------------+
| 1 |
+--------------+
mysql> select ifnull(null,10);
+------------------+
| ifnull(NULL, 10) |
+------------------+
| 10 |
+------------------+keywords
IFNULL