create table tbl ( id int);
insert into tbl values (1), (10), (10), (20), (2), (2), (10), (20);
select * from tbl;
create table tbl_uniq as select distinct id from tbl;
alter table tbl_uniq add primary key (id);
drop table tbl;
rename table tbl_uniq to tbl;
select * from tbl;