id int
title varchar

id int
parentid int  --主表的ID
filename varchar

select top 25 a.* from ta a join tb b on a.id=b.parentid 
where b.filename is not null or filename<>''

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SQL code
select top 25 a.* from tb a,tb b where a.id=b.id and b.filename is not null

------解决方案--------------------

SQL code
SELECT  TOP 25 a.* FROM  ta a,tb b WHERE a.id=b.parentid AND( b.filename is not null AND b.filename<>'')

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

select top 25 p.id,p.title,s.filename from temp_main as p inner join temp_detail as s
on p.id=s.parentid 
where filename is not null or filename<>''