A column or set of columns defined as UNIQUE must also be NOT NULL.
Teradata Database instantiates UNIQUE as a unique primary or secondary index. One or more columns or sets of columns can be defined as UNIQUE for a table.
For more details, see:
- “CREATE TABLE” in Teradata Vantage™ SQL Data Definition Language Syntax and Examples, B035-1144
- “Constraint Specifications” in Teradata Vantage™ - Database Design, B035-1094.