[PHP,MYSQL]ขอทราบวิธีลบฟิลด์ซ่ำในคอลั่ม SQL[ขอบคุณครับ]

alter table `yourtable` add field_tmp integer;
#==========================

update `yourtable` tb1 
left join (select min( `primary_key`) tmp_id from `yourtable` group by `search_field` ) tb2
on tb2.`tmp_id` = tb1.primary_key
set tb1.field_tmp=1 where tb2.tmp_id is not null;
#==========================

delete from `yourtable` where field_tmp < 1;
#==========================

alter table `yourtable` drop field_tmp;