使用Linq to SQL确定行是否存在的最快方法是什么? [英] What is the fastest way to determine if a row exists using Linq to SQL?

问题描述

我对一行的内容不感兴趣，我只想知道一行是否存在. Name列是主键，因此将有0或1个匹配的行.目前，我正在使用:

if ((from u in dc.Users where u.Name == name select u).Count() > 0)
    // row exists
else
    // row doesn't exist

尽管上述方法有效，但通过选择该行的所有内容(如果存在)，它做了很多不必要的工作.以下内容是否会创建更快的查询:

if (dc.Users.Where(u => u.Name == name).Any())

...还是有更快的查询?

Count()方法可能会做额外的工作，因为(在TSQL中)EXISTS或TOP 1通常更快.数据库可以优化至少有一行".就个人而言，我将使用any/predicate重载:

if (dc.Users.Any(u => u.Name == name)) {...}

当然，您可以通过观察TSQL来比较每个人的工作:

dc.Log = Console.Out;

I am not interested in the contents of a row, I just want to know if a row exists. The Name column is a primary key, so there will either be 0 or 1 matching rows. Currently, I am using:

if ((from u in dc.Users where u.Name == name select u).Count() > 0)
    // row exists
else
    // row doesn't exist

While the above works, it does a lot of unnecessary work by selecting all the contents of the row (if it exists). Does the following create a faster query:

if (dc.Users.Where(u => u.Name == name).Any())

...or is there an even faster query?

解决方案

The Count() approach may do extra work, as (in TSQL) EXISTS or TOP 1 are often much quicker; the db can optimise "is there at least one row". Personally, I would use the any/predicate overload:

if (dc.Users.Any(u => u.Name == name)) {...}

Of course, you can compare what each one does by watching the TSQL:

dc.Log = Console.Out;

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