UNIQUE

A specific field or set of fields must be unique.

CREATE TABLE SchameName.TableName(
	ColName1 smallint IDENTITY(1,1) NOT NULL,
	ColName2 VARCHAR(50),
	CONSTRAINT uq_ColName1_ColName2 UNIQUE(ColName1, ColName2)
)

CREATE TABLE SchameName.TableName(
	ColName1 smallint IDENTITY(1,1) NOT NULL,
	ColName2 VARCHAR(50) UNIQUE,
)