You can define a unitext column the same way you define other datatypes, using create table or alter table statements. You do not define the length of a unitext column, and the column can be null.
This example creates a unitext column that allows null values:
create table tb (ut unitext null)
default unicode sort order defines the sort order for unitext columns for pattern matching in like clauses and in the patindex function, this is independent of the Adaptive Server default sort order.
