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ef 查询总结

2024-08-11 20:09:35   216人阅读

1、Linq 查询两张表；a表和b表，要得到的数据是a表数据b表没有

例如：a表有5条数据1,2,3,4,5；b表有2条数据1,3；那么就用dataGridView1输出2,4,5；link语句要怎么写

 

from x in a where !b.Any(y=>y.id==x.id) select x;

 

------------------------------------- 转化成的sql类似如下 

SELECT [t0].[ID] AS [ID] FROM [a] AS [t0] WHERE NOT (EXISTS( SELECT NULL AS [EMPTY] FROM [b] AS [t1] WHERE [t1].[ID] = [t0].[ID] ))

 

这样b表中没有的就输出了。

2、Linq获取两个List或数组的差集交集

List<int> list1 = new List<int>();list1.Add(1);list1.Add(2);list1.Add(3);List<int> list2 = new List<int>();list2.Add(3);list2.Add(4);list2.Add(5);//得到的结果是4,5 即减去了相同的元素。List<int> list3 = list2.Except(list1).ToList();foreach (int i in list3){    MessageBox.Show(i.ToString());}

合并两个数组,并去掉重复元素,然后排序(C#)

List<int> numbers1 = new List<int>() { 5, 4, 1, 3, 9, 8, 6, 7, 12, 10 };List<int> numbers2 = new List<int>() { 15, 14, 11, 13, 19, 18, 16, 17, 12, 10 };var newQuerty = numbers1.Concat(from n in numbers2where !numbers1.Contains(n)select n).OrderBy(n=>n);

合并两个数组，并去除合并后的重复数据， 并排序

  int[] A={1,2,2,3,4,5,6,6,6};            int[] B={2,2,2,3,7,8,9,5};            List<int> list = new List<int>(A);            list.AddRange(B);            list.Sort();            //去除重复项            foreach (int i in list.Distinct<int>())            {                Console.WriteLine(i);            }

C# 取两个数组的相同元素

以往我们都是肯定绞尽脑汁，肯定什么循环，元素大小，什么因素都考虑进去。但是现在采用Linq可以很好的解决这个问题。找出两个或多个数组的相同项。

代码相当简单：

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text; namespaceTest4_03{   classProgram    {       staticvoidMain(string[] args)        {           string[] names = {"Adams","Arthur","Buchanan","Tsbuchis","ShCian","FuchsiaLinda","DecheChen","Lotheer","FindLanciCade","SorchLand","JiangZheng","MisiiLoda","Gtod","Dfac","Lama","BakCades","Losangle","ZheWQ","GehengDahaLothi","ToryLandey","DakaLothy","BthLanda","MenNorth","Fith","FoxMain","DontM","Saobba","Del","Sala","Ghero","BhthLaPhda"};           IEnumerable<string> skip = names.Skip(10);           IEnumerable<string> take = names.Take(11);            //取出两个序列中交集部分，按理论应该输出JiangZheng           IEnumerable<string> intersect = skip.Intersect(take);            foreach(varsinintersect)            {               Console.WriteLine(s);            }           Console.ReadKey();        }    }}

 

ef 查询总结


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