SQL变量返回的时间比静态值长

Question

我有一个包含两个值的表:

ciid, businessdate

ciid是主键,并且已启用自动增量.businessdate(datetime)由另一个进程插入.

给出以下查询:

select top(1) ciid, businessdate
from checkitemsales 
where businessdate='10/9/16 00:00:00:000'

返回仅需1.2秒,而此查询:

declare @var1 datetime

set @var1='10/9/16 00:00:00:000'

select top(1) ciid, businessdate
from checkitemsales
where businessdate = @var1

返回需要5.6秒.

谁能告诉我我做错了什么？

Answer 1

declare @var1 datetime

set @var1='10/9/16 00:00:00:000'

select top(1) ciid, businessdate
from checkitemsales
where (businessdate = @var1) option (recompile)

试试这个，让我知道结果，可能会更快