Q: According to the RDB theory, NULL is different from spaces, and NULL must be used in some cases. However, there is no NULL data type in the program language, so how does NULL in the database? A: Read NULL: Field.isnull can determine if the specified static field is NULL. When assigning null: If you use Table.Insert, the unfameted field is assigned NULL. If you use Table.EDIT, Fiels.clear can assign a specified static field to null. If you use Query, follow the standard SQL statement.
