UNIQUE

Der Constraint UNIQUE versichert uns, dass alle Werte in einem Attribut einzigartig sind.

CREATE TABLE Persons (
    Id INTEGER NOT NULL,
    LastName VARCHAR(45) NOT NULL,
    FirstName VARCHAR(45),
    Age INTEGER,
    CONSTRAINT UQ_Person_LastName UNIQUE (LastName)
);

ALTER TABLE Persons
ADD CONSTRAINT UQ_Person_LastName UNIQUE (LastName);

ALTER TABLE Persons
DROP INDEX UQ_Person_LastName;