SQL での無効な重複行の削除

これを試してください:

 ;WITH users_CTE as (
 select rank() over (partition by Username order by Checktime) as rnk from users
 )

 DELETE FROM users_CTE where rnk <> 1

-- 2 番目の要件については、このクエリを試してください

 ;WITH users_CTE as (
 select *,rank() over (partition by Username order by Checktime) as rnk from users
 )
,CTE2 as (select Username,MIN(CheckTime) as minTime,DATEADD(mi,1,MIN(CheckTime)) as maxTime from users_CTE 
 group by Username)



delete from users where Checktime in(
select c1.Checktime from users_CTE c1 left join CTE2 c2
on c1.Checktime > c2.minTime and c1.Checktime <= c2.maxTime
where c2.Username is not null and c1.Username in(

select c1.Username from users_CTE c1 left join CTE2 c2
on c1.Checktime > c2.minTime and c1.Checktime <= c2.maxTime
group by c1.Username,c2.Username 
having COUNT(*) > 1))

-- 変更された要件については、以下のクエリを確認してください

alter table users add flag varchar(2)

;WITH users_CTE as (
 select *,rank() over (partition by Username order by Checktime) as rnk from users
 )
,CTE2 as (select Username,MIN(CheckTime) as minTime,DATEADD(mi,1,MIN(CheckTime)) as maxTime from users_CTE 
 group by Username)


update u SET u.flag = 'd' from users_CTE u inner join (
select c1.Checktime from users_CTE c1 left join CTE2 c2
on c1.Checktime > c2.minTime and c1.Checktime <= c2.maxTime
where c2.Username is not null and c1.Username in(

select c1.Username from users_CTE c1 left join CTE2 c2
on c1.Checktime > c2.minTime and c1.Checktime <= c2.maxTime
group by c1.Username,c2.Username 
having COUNT(*) > 1)) a
on u.Checktime=a.Checktime

--DeletFlagで最新のクエリを確認

;WITH users_CTE as 
(
 select *,row_number() over (partition by Username order by Checktime) as row from users
)
,CTE as(
select row,Username,Checktime,CheckType,0 as totalSeconds,'N' as Delflag from users_CTE where row=1 
union all
select t.row,t.Username,t.Checktime,t.CheckType,CASE WHEN (c.totalSeconds + DATEDIFF(SECOND,c.Checktime,t.Checktime))  >= 60 then 0 else (c.totalSeconds + DATEDIFF(SECOND,c.Checktime,t.Checktime)) end as totalSeconds,
CASE WHEN (c.totalSeconds + DATEDIFF(SECOND,c.Checktime,t.Checktime))  >= 60 then 'N' else 'Y' end as Delflag
--CASE WHEN c.totalSeconds <= 60  then 'Y' else 'N' end as Delflag
from users_CTE t inner join CTE c
on t.row=c.row+1
)

select Username,Checktime,CheckType,Delflag from CTE