By understanding the difference between IN, EXISTS, NOT IN, and NOT EXISTS, you can avoid a very common problem when NULLs appear in the data of a subquery. Scott Stephens helps you understand ...

IS NULL and IS MISSING are predicates that test for a missing value. IS NULL and IS MISSING are used in the WHERE, ON, and HAVING expressions. Each predicate resolves to true if the sql-expression's ...

If you do, you'll have a problem at runtime. But -- and this is so important -- you'll be notified of the problem not when the null pointer is used, which could be a long way from the mistaken code ...