Saving space by allowing NULL

To save storage space for empty text or image columns, define them to permit null values and insert nulls until you use the column. Inserting a null value does not initialize a text or image column and, therefore, does not create a text pointer or allocate storage. For example, the following statement inserts values into the title_id and pub_id columns of the testtext table created above, but does not initialize the blurb text column:

insert texttest
(title_id, pub_id) values ("BU7832", "1389")

After a text or image row is given a non-null value, it always contains at least one data page. Resetting the value to null does not deallocate its data page.