create table tb(单号 int,条码 varchar(10),送修时间 datetime,维修完成时间 datetime)
insert into tb select 1,'A','2011-10-9','2011-10-10'
insert into tb select 2,'A','2011-10-15','2011-10-31'
insert into tb select 3,'A','2011-12-16','2011-12-30'
insert into tb select 4,'B','2011-9-10','2011-9-15'
insert into tb select 5,'B','2011-11-10','2011-11-20'
insert into tb select 6,'C','2011-12-1','2011-12-3'
insert into tb select 7,'C','2011-12-5','2011-12-6'
go
select * from tb a 
where exists(select 1 from tb where 条码=a.条码 and 单号<>a.单号 and abs(datediff(d,送修时间,a.维修完成时间))<30)
/*
单号          条码         送修时间                    维修完成时间
----------- ---------- ----------------------- -----------------------
1           A          2011-10-09 00:00:00.000 2011-10-10 00:00:00.000
2           A          2011-10-15 00:00:00.000 2011-10-31 00:00:00.000
6           C          2011-12-01 00:00:00.000 2011-12-03 00:00:00.000
7           C          2011-12-05 00:00:00.000 2011-12-06 00:00:00.000

(4 行受影响)

*/
go
drop table tb