TSQL: Unique Constraint

To add a UNIQUE constraint to a column in a table:

ALTER TABLE {TableName} ADD CONSTRAINT {ConstraintName} UNIQUE({UniqueColumnName})

Such as:

ALTER TABLE Department ADD CONSTRAINT UNIQUE_DepartmentName UNIQUE (NAME)

To add a UNIQUE constraint to two columns in a table:

ALTER TABLE {TableName} ADD CONSTRAINT {ConstraintName} UNIQUE
({UniqueColumnName1},{UniqueColumnName2})

Such as:

ALTER TABLE Department ADD CONSTRAINT UNIQUE_DepartmentNameRoom
UNIQUE(NAME,RoomNumber)