Limitations for Nonmaterialized Columns

alter table … modify does not support converting existing materialized columns to nonmaterialized columns. Running alter table ... modify against a column instantiates all nonmaterialized columns in the table.

You cannot:

Use bit, text, image, unitext, and Java datatypes in nonmaterialized columns.
Use nonmaterialized columns as IDENTITY columns.
Include the constraint, primary key, unique, or references clauses when you use alter table to add nonmaterialized columns.
Encrypt nonmaterialized columns.
Downgrade an SAP ASE server using data rows with nonmaterialized, non-NULL columns to versions earlier than 15.7. You must first run reorg rebuild on tables containing these columns to convert them to regular, non-nullable columns, before downgrading your SAP ASE server.