select count(1) from tab a
where not exists (
   select 1 from tab 
   where 号码=a.号码 and 产生时刻 between a.产生时刻 and dateadd(ss,20,a.产生时刻)
   )

------解决方案--------------------
SQL code

create table #t(dt datetime,col int)
insert into #t values('2007-2-7   14:31:17',1234)
insert into #t values('2007-2-7   14:31:20',1234)
insert into #t values('2007-2-7   14:33:12',1544)
insert into #t values('2007-2-7   14:41:10',1111)


select count(1) from #t a where not exists (select 1 from #t where dt>a.dt and dt<=dateadd(ss,20,a.dt)  and col=a.col)


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3

(1 行受影响)