PRIMARY KEY Constraints Versus UNIQUE Constraints
UNIQUE and PRIMARY KEY constraints can only be defined on a column set that is also constrained to be NOT NULL.
To create a composite, or multicolumn, primary key for a table, you must specify the PRIMARY KEY constraint at the table level, not the column level.
Both UNIQUE and PRIMARY KEY constraints can be defined on a UDT column.
Teradata Database also supports the related constraints UNIQUE INDEX and UNIQUE PRIMARY INDEX.