Data Definition Language (DDL) Reference Manual

Definition Attributes

Data Definition Language (DDL) Reference Manual—529431-004

6-19

NULL

The NULL clause assigns a null value to a field or group used as an Enscribe alternate

key. If a record being inserted in the database has a null value in the alternate key

field, the alternate key is not added to the alternate key file.

character

is any ASCII character.

number

is any number from 0 through 255.

constant-name

is the name of a constant in the open dictionary. The constant value must be a

valid character or number value.

Any alternate key can be assigned a null value. The most common null values are

ASCII blank (%40) and binary zero. The null value used must fit in one byte.

When you generate FUP source code from the DDL definition, the FUP code specifies

alternate key file information, including the octal representation of the null value you

select.

The file system checks records as they are inserted in the file to see if the value in the

alternate key field matches the null value. The effects of using a null value are:

•

When records are inserted, if the record has an alternate key with a null value, the

key is not added to the alternate key file.

•

When records are updated, any alternate key with a null value is deleted from the

alternate key file.

•

If a file is read sequentially by an alternate key, any record with a null value for that

alternate key is not found.

In Example 6-15 on page 6-20, if the employee does not have a spouse or

dependents, the key is not added to the alternate key file.

Note. The DDL compiler ignores this clause when generating host-language source code.

NULL { "character " | number | constant-name }