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 ...

One of the trickiest aspects of relational database management can be dealing with missing information. The standard method of representing missing information is to set the 'value' to null.

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 ...