我应该使用哪个查询来提高性能？ [英] Which Query Should i Use for Better Performance?

问题描述

大家好......

我正在尝试优化存储过程...在Sp中有一些4-5 If exists语句。

Hi All...
I Am Trying to Optimize the Stored Procedure... in the Sp there are some 4-5 If exists Statements.

If exists(Select * From TableName)
 --Do Something
Else
 -- Do SomeThimg

我可以替换那些如果存在带

If (Select Count(*) From TableName)>0
 -- Do Something
Else
 -- Do Something

我的问题是哪个会执行得更快..？

我使用此代码由一些人编写否则检查查询

My Question is Which Will execute faster..?
I Used This Code Written by Some one Else to Check the Queries

Declare @cpu_ int
Declare @lreads_ int
Declare @eMsec_ int

Select @cpu_ = cpu_time
, @lreads_ = logical_reads
, @eMsec_ = total_elapsed_time
 From sys.dm_exec_requests
 Where session_id = @@spid

--======
-- Your Test Code Goes Here
--======

Select cpu_time-@cpu_ as CpuMs
, logical_reads- @lreads_ as LogRds
, total_elapsed_time - @eMsec_ as Elapsed
 From sys.dm_exec_requests
 Where session_id = @@spid

但我得到相同的结果（即相同的LogRds，CpuMs，Elapsed对于 IF存在和如果（选择）> 0

如果我使用 SET STATISTICS IO ON

我得到输出

But I get the Same Results(i.e. Same LogRds,CpuMs,Elapsed For both IF exists and If (Select)>0
If I Use SET STATISTICS IO ON
I get the Output

Table 'TableName'. Scan count 1, logical reads 3, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'TableName'. Scan count 1, logical reads 3, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

可以任何人建议我应该使用哪一个..？



谢谢

Raj ..

Can Any one Suggest which one Should i Use..?

Thanks
Raj..

推荐答案

试试这个：

Try this:

If exists(Select 1 From TableName)

If exists(Select TOP(1) 1 From TableName)

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