如何优化此T-sql查询？

Question

There is a loop in this query, in the last where condition. and this causes a severe problem to the performance of SQL.

I have no idea about how to modify it.

select pr.tavpun
 from mta110 pr
 where pr.taisoc = mta110.taisoc
   and pr.taitar = mta110.taitar
   and pr.taydat = mta110.taydat
   and pr.tairef = mta110.tairef
   and pr.tatind = (select max(pr2.tatind) from mta110 pr2
                    where pr2.taisoc = mta110.taisoc
                      and pr2.taitar = mta110.taitar
                      and pr2.taydat = mta110.taydat
                      and pr2.tairef = mta110.tairef
                      and pr2.tatind <= mgc100.gntind)) AS SalesPrice

Answer 1

Your query makes little sense, because pr is not a reasonable alias for mta110 , and mta110 is not recognized in the outer query.

I speculate that you have two tables, pr and mta110 which are joined and you want the "most recent" row of mta110 for each matching row.

If this interpretation is correct, then you can use row_number() and a proper join :

select . . .
from pr join
     (select m.*,
             row_number() over (partition by taisoc, taitar, taydat, tairef order by gntind desc) as seqnum
      from mta110 m
     ) m
     on pr.? = m.?
where seqnum = 1;