Because a null is not a value it is not greater than, less than, or equal to any other value. And one null does not equal another null. It is invalid to test if a column is = NULL, < NULL, <= NULL, > ...

Many developers try to use references as much as they can because references can't be null, but you can't re-home a reference and get it to refer to something different, as you can with a pointer. So ...

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 ...