SELECT TOP 100 PERCENT
        dbo.hyxx.hykh, dbo.hyxx.hyxm, dbo.hyxx.klxmc, dbo.hyxx.kmc, dbo.hyxx.jrrq, dbo.hyxx.yddh, dbo.hyxx.hyjf, x.xfrq, x.fdid, x.hyfdid, x.xfje, dbo.hyxx.hyje
FROM    dbo.hyxx
LEFT JOIN dbo.xfxx x
ON      x.hykh = dbo.hyxx.hykh
WHERE   NOT EXISTS ( SELECT 1
                     FROM   xfxx
                     WHERE  hykh = hyxx.hykh
                            AND xfrq > hyxx.xfrq )
ORDER BY dbo.hyxx.hykh DESC

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

SELECT TOP 100 PERCENT dbo.hyxx.hykh, dbo.hyxx.hyxm, dbo.hyxx.klxmc, 
  dbo.hyxx.kmc, dbo.hyxx.jrrq, dbo.hyxx.yddh, dbo.hyxx.hyjf, x.xfrq, x.fdid, x.hyfdid, 
  x.xfje, dbo.hyxx.hyje
FROM dbo.hyxx LEFT JOIN
  dbo.xfxx x ON x.hykh = dbo.hyxx.hykh
  outer apply (SELECT TOP 1 id
               FROM xfxx
               WHERE hykh = hyxx.hykh
               ORDER BY xfrq DESC)) d
WHERE x.id = d.id
ORDER BY dbo.hyxx.hykh DESC

--try!

------解决方案--------------------
探讨

SQL code

SELECT TOP 100 PERCENT dbo.hyxx.hykh, dbo.hyxx.hyxm, dbo.hyxx.klxmc, 
  dbo.hyxx.kmc, dbo.hyxx.jrrq, dbo.hyxx.yddh, dbo.hyxx.hyjf, x.xfrq, x.fdid, x.hyfdid, 
  x.xfje, dbo.hyxx.hyje
FRO……


------解决方案--------------------
select a.hykh,c.hyxm,c.klxmc,c.kmc,c.jrrq,c.yddh,c.hyjf,B.xfrq,
 B.fdid,B.hyfdid,B.xfje,B.hyje
 from (select hykh,MAX(xfrq) xfrq from xfxx group by hykh) a
  left join xfxx b on a.hykh = B.hykh and a.xfrq = B.xfrq
  left join hyxx c on a.hykh = c.hykh

试试这样会不会快点