Restrictions for Modifying a Table Schema

Restrictions when modifying table schema.

You cannot run alter table from inside a transaction.
Altering a table’s schema can invalidate backups that you made using bcp. These backups may use a table schema that is no longer compatible with the table’s current schema.
You can add NOT NULL columns with check constraints, however, the SAP ASE server does not validate the constraint against existing data.
You cannot change the locking scheme of a table using the alter table . . . add, drop, or modify commands if the table has a clustered index and the operation requires a data copy. Instead you can
1. Drop the clustered index.
2. Alter the table’s schema.
3. Re-create the clustered index.
You cannot alter a table’s schema if there are any active open cursors on the table.