Use IS NOT NULL when a query should keep only rows where a column contains a value. For example, it can find authors who have a middle name. section 7.2.3
SELECT
FirstName,
MiddleName,
LastName
FROM author
WHERE MiddleName IS NOT NULL;
This query returns each author's first, middle, and last name only when MiddleName is not NULL. section 7.2.3
Read IS NOT NULL as “is not missing.” The predicate can also produce the same result as MiddleName LIKE '%' in this text-column example: the percent wildcard matches stored string data, while NULL represents no data. section 7.2.3
Preventing an incomplete promotion
A stored procedure can test IF _PromotionCode IS NOT NULL THEN before inserting a promotion. A supplied code allows the insert; passing NULL skips it, so the call with promotion ID 15 produces no row. section 21.2.1
