# **ISNULL**

## **Grammar Description**

You can use the `ISNULL()` function instead of `=` to test whether the value is `NULL`. (Comparing the value with `NULL` using `=` always produces `NULL`.)

If the expression is `NULL`, the function returns `true`. Otherwise, it returns `false`.

The `ISNULL()` function shares some special behavior with the `IS NULL` comparison operator. See the description of [`IS NULL`](is-null.md).

## **Grammar Structure**

```text
> ISNULL(expr)
```

## **Example**

- Example 1:

```text
mysql> SELECT ISNULL(1+1);
+--------------------+
| isnull(1 + 1) |
+--------------------+
| false |
+--------------------+
1 row in set (0.01 sec)
```

- Example 2:

```text
CREATE TABLE students (id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(50) NOT NULL, birth_date DATE );

INSERT INTO students (name, birth_date) VALUES ('John Doe', '2000-05-15'), ('Alice Smith', NULL), ('Bob Johnson', '1999-10-20');

-- Use the ISNULL() function to find students who did not fill in their date of birth:
mysql> SELECT * FROM students WHERE ISNULL(birth_date);
+-------+--------------------------------+
| id | name | birth_date |
+-------+--------------------------------+
| 2 | Alice Smith | NULL |
+-------+--------------------------------+
1 row in set (0.00 sec)

-- The ISNULL() function can also use IS NULL to implement the same function, so the following query is also equivalent:
mysql> SELECT * FROM students WHERE birth_date IS NULL;
+-------+--------------------------------+
| id | name | birth_date |
+-------+--------------------------------+
| 2 | Alice Smith | NULL |
+-------+--------------------------------+
1 row in set (0.01 sec)
```