MySQL ISNULL()函数和IS NULL运算符有什么区别？

ISNULL()函数和IS NULL运算符在行为上有一些共同之处，主要的不同点在于它们的语法不同。ISNULL()函数的参数为表达式，而IS NULL运算符将表达式放在其左侧。否则，它们都会在表达式为空时返回1，否则返回0。下面的示例将说明上述概念。

mysql> Select 1 IS NULL;
+-----------+
| 1 IS NULL |
+-----------+
| 0         |
+-----------+
1行受影响 (0.00 sec)

mysql> Select ISNULL(1);
+-----------+
| ISNULL(1) |
+-----------+
| 0         |
+-----------+
1行受影响 (0.00 sec)

mysql> Select ISNULL(1/0);
+-------------+
| ISNULL(1/0) |
+-------------+
| 1           |
+-------------+
1行受影响 (0.00 sec)

mysql> Select 1/0 IS NULL;
+-------------+
| 1/0 IS NULL |
+-------------+
| 1           |
+-------------+
1行受影响 (0.00 sec)

mysql> Select * from Employee WHERE Salary IS NULL;
+----+-------+--------+
| ID | Name  | Salary |
+----+-------+--------+
| 7  | Aryan | NULL   |
| 8  | Vinay | NULL   |
+----+-------+--------+
2行受影响 (0.00 sec)

mysql> Select * from Employee WHERE ISNULL(Salary);
+----+-------+--------+
| ID | Name | Salary |
+----+-------+--------+
| 7  | Aryan | NULL   |
| 8  | Vinay | NULL   |
+----+-------+--------+
2行受影响 (0.00 sec)

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