This field allows you to specify whether the data column accepts null values. A null value is a special value that represents unknown or unavailable data. On standard installations, a null value appears to be an empty field, but there is a difference between a null value and a blank or a zero. A nullable column is one that accepts a null value. The Nulls field works in conjunction with the Defaults field.

To specify that the data column can accept null values, enter y in this field. If a user does not enter data into a nullable column, a value is entered for that column as specified by the Defaults field (as described in Column Specification--Defaults).

To specify that the column cannot accept null values, enter n. When a user does not enter data into a non‑nullable data column, either the value of zero (0) is automatically entered into the column if it is a numeric column, or the column is left blank if it is a character column, or the user is required to enter a value. Use the Defaults column in the Column Specification form to specify this choice.