declare @i varchar(10)='002'
if exists(select 1 from tb where beginno<@i and endno>@i)
print 
'@i 已经存在

------解决方案--------------------

SQL code
declare @a varchar(3)
set @a='002'
if exists (select 1 from tb where @a >beginno and @a<endno)
print '该数据已经存在了'
else
insert into tb ......