Null values

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dBASE Plus supports a special value represented by the keyword null. It is its own data type, and is used to indicate a nonexistent or undefined value. A null value is different from a blank or zero value; null is the absence of a value.

The new DBF7 (dBASE) table type support nulls, as do most other tables, including DB (Paradox). Older DBF formats do not. A null value in a field would indicate that no data has been entered into the field, like in a new row, or that the field has been emptied on purpose. In certain summary operations, null fields are ignored. For example, if you are averaging a numeric field, rows with a null value in the field are ignored. If instead a null value was considered to be zero or some other value, it would affect the average.

null is also used in dBASE Plus to indicate an empty function pointer, a property or variable that is supposed to refer to a function, but doesn’t contain anything.