Null means "undefined" in SQL, ... who is an expert in Adobe's ColdFusion web app server platform, states that null values should absolutely not be used in databases. ...

Null values indicate that data is missing or unknown, ... Excluding null values in a group . Jet SQL’s GROUP BY clause doesn’t eliminate null values from the grouped results.

When you use IN, you’re telling SQL to take a value and compare it against every value or set of values in a list using =. If any NULL values exist, a row will not be returned–even if both ...