sql删除重复条目只保留一条

delete from table_name where we_id not in 
(
select mid from (
select min(we_id) as mid from table_name group by fail_reason HAVING count(*) > 1
) k 
) 
and fail_reason in 
(
select fail_reason from (
select fail_reason    from table_name group by fail_reason HAVING count(*) > 1
) k1 
);