ISNULL
Checks whether a value is NULL.
MySQL 8.1
ISNULL(value)Parameters
- value
- Value to check
Return value
1 if the value is NULL, otherwise 0; an empty string and 0 are not NULL
Examples
NULL, zero and empty string
MySQL 8.1
SELECT ISNULL(NULL) AS null_value,
ISNULL(0) AS zero,
ISNULL('') AS empty_string;Checking middle name for NULL
MySQL 8.1
SELECT last_name,
middle_name,
ISNULL(middle_name) AS no_middle_name
FROM Teacher
WHERE id BETWEEN 9 AND 12;Details
The function only checks the value: ISNULL(x) is the same as x IS NULL. To replace NULL with another value, use IFNULL or COALESCE: in SQL Server ISNULL(a, b) replaces NULL, but in MySQL two arguments give an error. PostgreSQL has no such function; the check is written as x IS NULL.