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Null Values

ADABAS has a special value called a null value, which means an absence of information. A null value is analogous to the SAS System's missing value.

You can define data fields to not store null data by specifying the NU option in data definition statements. In normal data storage (that is, NU not specified), a null value is represented by two bytes (one for the value length and one for the null value). Suppressing null values results in a null value being represented by a one-byte empty field indicator. The null value itself is not stored.

Knowing whether a data field allows null values assists you in writing selection criteria and in entering values to update ADABAS data. For example, if the NU option is specified for an ADABAS descriptor data field, null values for the data field are not stored in the inverted list. Therefore, a search using this data field and for which a null value is the search value, would result in no records selected, even though there may be records that contain a null value for the data field.

For more information on null values, see Missing Values (Nulls).

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