優化where子句（短路）時，SQL Server 2008

Question

一個如何優化這個查詢：

declare @MyParam nvarchar(100) = 25846987; 

select top 100 * from MySelectTable 
where 
(MyParam = @MyParam) 
OR 
(@MyParam = 0 and MyParam in (SELECT MyParam FROM aMassiveSlowTable WHERE Id = 'random1')) 
OR 
(@MyParam = 1 and MyParam in (SELECT MyParam FROM aMassiveSlowTable WHERE Id = 'random2')) 
OR 
(@MyParam = 2 and MyParam in (SELECT MyParam FROM aMassiveSlowTable WHERE Id = 'random3')) 

當我只用這部分：

declare @MyParam nvarchar(100) = 25846987; 

select top 100 * from MySelectTable 
where 
(MyParam = @MyParam) 

它返回1秒。

使用所有參數時，大約需要5分鐘。

我相信這是因爲它只是在匹配MyParam = @MyParam時掃描一個MassiveSlowTable。

如果@MyParam匹配MyParam，我該如何跳過所有其他比較？我嘗試使用CASE語句，但它們不適用於IN子句。我嘗試重新排列並列中的AND，甚至在aMassiveSlowTable中添加額外的過濾。

如果@MyParam與MyParam不匹配，則查詢花費一點時間就可以。

Answer 1

這可能會解決它
在它應該得到評估早期

(MyParam in (SELECT MyParam FROM aMassiveSlowTable WHERE Id = 'random1' and @MyParam = 0)) 

或

declare @MyParam nvarchar(100) = 25846987; 
select * 
from MySelectTable 
where MyParam = @MyParam 
union 
select * 
from MySelectTable 
join aMassiveSlowTable as Slow 
and Slow.MyParam = MySelectTable.MyParam 
and Slow.ID = 'random0' 
where @MyParam = 0 
union 
select * 
from MySelectTable 
join aMassiveSlowTable as Slow 
and Slow.MyParam = MySelectTable.MyParam 
and Slow.ID = 'random1' 
where @MyParam = 1 
union 
select * 
from MySelectTable 
join aMassiveSlowTable as Slow 
and Slow.MyParam = MySelectTable.MyParam 
and Slow.ID = 'random2' 
where @MyParam = 2 

或與該聯接提示

declare @MyParam nvarchar(100) = 25846987; 
select top 100 * 
from MySelectTable 
left join aMassiveSlowTable as Slow 
    on Slow.MyParam in (1,2,3) -- now the optimizer has something hard to evalate 
and Slow.MyParam = MySelectTable.MyParam 
or (Slow.MyParam = 0 and Slow.ID = 'random0') 
or (Slow.MyParam = 1 and Slow.ID = 'random1') 
or (Slow.MyParam = 2 and Slow.ID = 'random2') 
where MyParam = @MyParam 

Answer 2

發揮到性能方面的問題「使用所有參數時」你當你運行一個包含相關的查詢和謂詞在SQL Server 2008或SQL Server 2008 R2或SQL Server 2012中

http://support.microsoft.com/kb/2658214