图1为Count结果,用了35秒,哇塞!
图2为Where(条件).Count()结果,同样的数据只用了4秒钟,差了10倍!
然后为了取值方面我还是加入三元运算,ContentStatus=Product_Maintain.Where(C => C.CompanyID == company.ID && C.IsDeleted == 0 && (C.AuditStatus == 0 || C.AuditStatus == 4)).Count()>0?"产品有更新":""。结果如下:
真的是Count()与 Where()区别,不可能这么大差距吧?于是我单写 Product_Maintain.Where(C => C.IsDeleted == 0 && (C.AuditStatus == 0 || C.AuditStatus == 4)).Count() 与 Product_Maintain.Count(C => C.IsDeleted == 0 && (C.AuditStatus == 0 || C.AuditStatus == 4)) 发现速度差不多,生成的代码是一样的。
代码如下:
SELECT COUNT(*) AS [value]
FROM [GasSNS_Company_Equipment_Maintain] AS [t0]
WHERE ([t0].[IsDeleted] = @p0) AND (([t0].[AuditStatus] = @p1) OR ([t0].[AuditStatus] = @p2))
原来是我如果在Select中取某表的数量并且条件中使用了之前from后的某个变量时,这时用Count(条件)和Where(条件).Count()产生代码才会不同,查询速度才会出现数量级的差别。
代码
代码如下:
//效率低版本:
from company in Company
select new
{
contacter = v.ContacterID,
count = Product_Maintain.Count(C => C.CompanyID == company.ID &&C.IsDeleted == 0 && (C.AuditStatus == 0 || C.AuditStatus == 4))
}
与
代码如下:
//效率高版本:
from company in Company
select new
{
contacter = v.ContacterID,
count = Product_Maintain.Where(C =>C.CompanyID == company.ID && C.IsDeleted == 0 && (C.AuditStatus == 0 || C.AuditStatus == 4)).Count()
}
否则,Count()与Where().Count()生成的SQL语句是相同的,效率也一样。 总结到此,望各位看官以后要注意!本人入园两年来,第一发在首页,请各位看官不吝赐教! 谢谢各位看官的指点,声明下以上查询图都LinqPad查询结果截图。至于为啥4秒左右为LinqPad查询时间,Linq生成Sql语句在Sql Server中执行不到1秒,以下截图作解释:
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