Based on the database configuration, the functioning of the like and not like operators are case-sensitive or case-insensitive.
For example, if your database configuration is case-sensitive, string such as 'A%' matches with 'Abc' and not with 'abc'. If your database configuration is case-insensitive, string such as 'A%' matches with both 'Abc' and 'abc'.
Contact attributes with null value are not selected when the not in operator is used.