You cannot use an ALTER TABLE statement to add, modify, or drop the block-level compression characteristics of a table or join index. You must use the Ferret utility to change the block-level compression of a table or join index. See Teradata Vantage™ - Database Utilities, B035-1102. For a description of the restrictions on specifying block-level compression for volatile and global temporary tables, see Block-Level Compression and Tables.