Q3: Find employees who do not have a manager assigned.

Q3: Find employees who do not have a manager assigned.

In this query, we want to find employees who do not have a manager assigned.

We select all columns from the employees table and use:

WHERE manager_id IS NULL

Notice that we don’t use manager_id = NULL.

SELECT *
FROM employees
WHERE manager_id IS NULL;

In SQL, NULL represents a missing or unknown value, so we use the special operators IS NULL or IS NOT NULL to check for it.

In our result, we get 12 employees whose manager_id is NULL.

These are the top-level employees in our sample data, such as James Anderson, the Engineering Manager, Emily Davis, the Sales Manager, and Robert Moore, the Finance Manager.

The other employees have a manager_id that points to another employee.

So remember: whenever you need to find missing values in SQL, use IS NULL.

And when you want to find records where a value exists, use IS NOT NULL.