text, unitext, and image Columns

text, unitext, and image columns created with insert and NULL are not initialized and contain no value. They do not use storage space and cannot be accessed with readtext or writetext.

When a NULL value is written in a text, unitext, or image column with update, the column is initialized, a valid text pointer to the column is inserted into the table, and a 2K data page is allocated to the column. Once the column is initialized, it can be accessed by readtext and writetext. See the Reference Manual: Commands.