Syntax
ISNULL(expr)
Purpose
If the expr parameter is NULL, the return value of ISNULL() is 1; otherwise, the return value is 0.
The ISNULL() function can be used to determine whether a value is NULL instead of using the equal sign (=). (Using the equal sign to compare a value with NULL always returns NULL.) The ISNULL() function shares some characteristics with the IS NULL comparison operator. For more information about comparison operators, see Comparison operators.
Examples
obclient> SELECT ISNULL(null), ISNULL('test'), ISNULL(123.456), ISNULL('10:00');
+--------------+----------------+-----------------+-----------------+
| ISNULL(null) | ISNULL('test') | ISNULL(123.456) | ISNULL('10:00') |
+--------------+----------------+-----------------+-----------------+
| 1 | 0 | 0 | 0 |
+--------------+----------------+-----------------+-----------------+
1 row in set
obclient> SELECT ISNULL(null+1);
+----------------+
| ISNULL(null+1) |
+----------------+
| 1 |
+----------------+
1 row in set