3

建立一个查询。

单个查询如下所示，运行时间为 7.0 秒。它确实返回正确的答案。需要根据特定条件对行数进行计数，然后得到最大计数。我的问题是这种支持查询的性能。包裹在游标中的相同查询是 0.15 秒。在游标中，查询计划有很大不同。如何使独立查询运行得更快？

使用提示能够让独立计划看起来像光标计划，并解决了速度问题。

固定查询：（并非一直固定为 OPTION 失败）

select max(list.match) as 'max'
  from
  (
      SELECT 
       count(*) as 'match'  
      FROM [docSVenum1] with (nolock)   
      INNER LOOP JOIN  [FTSindexWordOnce] as w1 with (NOLOCK, FORCESEEK) 
        ON [docSVenum1].sID = w1.[sID] and [docSVenum1].[enumID] = '142'
      INNER HASH JOIN [FTSindexWordOnce] as w2 with (NOLOCK)
        ON  w1.wordID = w2.wordID and w2.[sID] = '2'      
      GROUP BY W1.[sID]
      -- OPTION (HASH GROUP)
  ) as list;

问题查询：

select getdate();
go
  select max(list.match) as 'max'
  from
  (
      SELECT 
       count(*) as 'match'
      FROM [FTSindexWordOnce] as w1 with (nolock)
      INNER JOIN [docSVenum1] with (nolock)
        ON [docSVenum1].sID = w1.[sID] and [docSVenum1].[enumID] = '142'
      INNER JOIN [FTSindexWordOnce] as w2 with (nolock)
        ON  w1.wordID = w2.wordID AND w2.[sID] = '2'
      GROUP BY W1.[sID]
  ) as list;
go
select getdate();   -- 7.0 seconds

我还需要针对多个值运行该单个查询并将其放入带有循环的游标中。我知道光标不好，但我不知道如何在没有光标的情况下做到这一点。

该查询独立且在循环内都返回相同的正确答案。

令我惊讶的是，游标循环中完全相同的查询要快 40 倍。

DECLARE @sid int

DECLARE sID_cursor CURSOR FOR 
SELECT top 80 sID
FROM docSVsys
WHERE sID = '2'  -- actually I want to not have this and let it loop through all
                 -- when i built the loop i saw performance improvement
ORDER BY sID

OPEN sID_cursor

FETCH NEXT FROM sID_cursor
INTO @sID

WHILE @@FETCH_STATUS = 0
BEGIN
    PRINT @sID

  select max(list.match) as 'max'
  from
  (
      SELECT 
       count(*) as 'match'
      FROM [FTSindexWordOnce] as w1 with (nolock)
      INNER JOIN [docSVenum1] with (nolock)
        ON [docSVenum1].sID = w1.[sID] and [docSVenum1].[enumID] = '142'
      INNER JOIN [FTSindexWordOnce] as w2 with (nolock)
        ON  w1.wordID = w2.wordID AND w2.[sID] = @sID
      GROUP BY W1.[sID]
  ) as list

    FETCH NEXT FROM sID_cursor
    INTO @sID

END 
CLOSE sID_cursor;
DEALLOCATE sID_cursor;
go
select getdate();  -- 0.15 seconds
4

1 回答 1

1

使用提示能够让独立计划看起来像光标计划，并解决了速度问题。

固定查询：（并非一直固定为 OPTION 失败）

select max(list.match) as 'max'
  from
  (
      SELECT 
       count(*) as 'match'  
      FROM [docSVenum1] with (nolock)   
      INNER LOOP JOIN  [FTSindexWordOnce] as w1 with (NOLOCK, FORCESEEK) 
        ON [docSVenum1].sID = w1.[sID] and [docSVenum1].[enumID] = '142'
      INNER HASH JOIN [FTSindexWordOnce] as w2 with (NOLOCK)
        ON  w1.wordID = w2.wordID and w2.[sID] = '2'      
      GROUP BY W1.[sID]
      -- OPTION (HASH GROUP)
  ) as list;
于 2012-07-29T17:37:50.337 回答