alter table b_iblock_element_prop_s80 modify column PROPERTY_444 varchar(255) not null;
ALTER TABLE b_iblock_element_prop_s80 ADD UNIQUE (PROPERTY_444);

отменить

ALTER TABLE b_iblock_element_prop_s80 DROP INDEX PROPERTY_444;
alter table b_iblock_element_prop_s80 modify column PROPERTY_444 text;