Question

我正在使用sql server 2008 r2并且具有以下查询

select * from
(        
    select d.ID as ID,
           ....
           ....        
           ROW_NUMBER() OVER 
           (
                ORDER BY #some field                           
           ) AS RowNum
    from
    /*some table*/
    LEFT join 
    (select Device_ID,          
            Level,          
            ROW_NUMBER() over (partition by Device_ID order by id desc) as rn
     from #sometable as de WITH (NOLOCK)
     where #some condition
     ) t
     where t.rn = 1)tmp on ID=tmp.Device_ID **/* sort operation 1*/**
     /*some more joins */
     WHERE /*some condition*/
) as DbD
where RowNum BETWEEN @SkipRowsLocal and (@SkipRowsLocal + @TakeRowsLocal - 1)
order by RowNum

我正在尝试从示例中实现分页类型的查询 http://blog.sqlauthority.com/2013/04/14/sql-server-tricks-for-row-offset-and-paging-in-various-versions-of-sql-server/

但看起来它的执行速度很慢，当我查看查询计划排序操作消耗了近50％的查询时间时，我猜它是我标记为1的第一个排序操作，基本上在临时表中我想要检索我想获取的最新值和外行数只能说40条记录。

它基本上就像排序10K行然后从中排出40行，我们有什么办法可以改进这个查询吗？

Answer 1

而不是左连接，尝试OUTER APPLY，以获得您感兴趣的设备的TOP 1 - 将其视为＆＃39;我从第一个表中获取记录，然后为该记录，我去另一个表中获取该设备ID的TOP 1，但记住在第二个表中，您需要搜索第一个表中的数据，而不是连接

    select * from
        (        
         select    d.ID as ID,
                   ....
                   ....        
                   ROW_NUMBER() OVER 
                   (
                        ORDER BY #some field                           
                    ) AS RowNum
            from
            /*some table*/
            OUTER APPLY
            (select TOP 1 Device_ID,          
                    Level          

                        from #sometable as de WITH (NOLOCK)
                        where #some condition and Device_ID = [/*some table*/].id ORDER BY id DESC
            ) t
            )tmp 
            /*some more joins */
            WHERE /*some condition*/
       ) as DbD
       where RowNum BETWEEN @SkipRowsLocal and (@SkipRowsLocal + @TakeRowsLocal - 1)
       order by RowNum

在这些行上的某些内容，您可能只想构建查询的相关部分并进行比较，它似乎会避免排序并且索引可能很快

优化行号查询

1 个答案: