MySQL ISNULL()函数和IS NULL运算符有什么区别？
重要的是，ISNULL()函数和ISNULL运算符都没有任何区别，并且具有一些共同的行为。我们可以看到的唯一区别是它们的语法。ISNULL()函数将表达式作为参数，而ISNULL比较运算符将表达式放在其左侧。否则，如果表达式为NULL，则两者都返回1；如果表达式为非NULL，则两者都返回0。以下示例将演示上述概念-
mysql> Select 1 IS NULL; +-----------+ | 1 IS NULL | +-----------+ | 0 | +-----------+ 1 row in set (0.00 sec) mysql> Select ISNULL(1); +-----------+ | ISNULL(1) | +-----------+ | 0 | +-----------+ 1 row in set (0.00 sec) mysql> Select ISNULL(1/0); +-------------+ | ISNULL(1/0) | +-------------+ | 1 | +-------------+ 1 row in set (0.00 sec) mysql> Select 1/0 IS NULL; +-------------+ | 1/0 IS NULL | +-------------+ | 1 | +-------------+ 1 row in set (0.00 sec) mysql> Select * from Employee WHERE Salary IS NULL; +----+-------+--------+ | ID | Name | Salary | +----+-------+--------+ | 7 | Aryan | NULL | | 8 | Vinay | NULL | +----+-------+--------+ 2 rows in set (0.00 sec) mysql> Select * from Employee WHERE ISNULL(Salary); +----+-------+--------+ | ID | Name | Salary | +----+-------+--------+ | 7 | Aryan | NULL | | 8 | Vinay | NULL | +----+-------+--------+ 2 rows in set (0.00 sec)