UNIQUE INDEX

CREATE UNIQUE INDEX index_name
    ON TABLE_NAME ( поля через запятую)

CREATE TABLE IF NOT EXISTS `NEW` (
  `ID` INT(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`ID`),
  UNIQUE KEY `UKEY` (`ID_A`,`ID_N`,`ID_B`,`ID_S`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=514240 ;