Problem w/Update table alter column unique

[ARyKaXaN]

hi every one.


well i'm newbie, so i have this problem, i want to update a field already containing LIVE data, so the properties from that particular field is text, but i want to add the unique property to that field, I tryed this;
mysql> alter table uno ADD CONSTRAINT UniqueValues UNIQUE(serie);

where uno is da table, and serie is the column i want to modify. i also try this;

mysql> ALTER TABLE uno MODIFY serie text NOT NULL unique(serie);

but neither works, can anyone helpme with this?

thanx