Linq的执行效率及优化

Posted 2021-01-07 zhao123

描述：项目中使用了linq，发现写的顺序不一样最后的结果也不一样，效率也不一样。

Linq的执行效率对比

List<int> source = new List<int>();
var rand = new Random();
int i = 5000;
while (i > 0)
{
    i--;
    source.Add(rand.Next(1, 500));
}

Stopwatch watch = new Stopwatch();

watch.Restart();
var temp2 = from s in source orderby s where s > 100 select s;
int count2 = temp2.Count();
watch.Stop();
Console.WriteLine("orderby s where s > 100: " + watch.ElapsedTicks);

watch.Restart();
var temp1 = from s in source where s > 100 orderby s select s;
int count = temp1.Count();
watch.Stop();
Console.WriteLine("where s > 100 orderby s: " + watch.ElapsedTicks);

效果如图：

效率相差还是蛮大的，差不多10倍，所以linq的执行要按照一定的顺序，不能随心所欲。

Linq优化

linq和sql的语法差不多，所以可以按照sql的执行顺序对linq进行优化，建议顺序

1.FROM
2.WHERE
3.GROUP BY
4.HAVING
5.SELECT
6.DISTINCT
7.UNION
8.ORDER BY