Foreign Key

Allows you to point at another table’s index for fast referencing.

CREATE TABLE SchameName.TableName(
	ColName1 smallint IDENTITY(1,1) NOT NULL PRIMARY KEY,
	ColName2 VARCHAR(50) UNIQUE,
	CONSTRAINT FK_ColNameId
	FOREIGN KEY (ColName2)
	REFERENCES SchemaName.OtherTable(ColName2) -- composite would be (ColName2, ColName3)
		ON DELETE CASCADE      -- or SET NULL / SET DEFAULT / NO ACTION (default)
    ON UPDATE NO ACTION;   -- CASCADE exists but use sparingly
)

ALTER TABLE SchemaName.TableName
	ADD CONSTRAINT FK_ColNameId
	FOREIGN KEY (ColNameId)