The null condition tests for nulls, when a value is missing or unknown.
expression IS [ NOT ] NULL
Any expression such as a column.
- IS NULL
Is true when the expression's value is null and false when it has a value.
- IS NOT NULL
Is false when the expression's value is null and true when it has a value.
This example indicates how many times the SALES table contains null in the QTYSOLD field:
select count(*) from sales where qtysold is null; count ------- 0 (1 row)