如何在LINQ中使用union all？

Question

如何在LINQ TO SQL中使用union all。 我已经使用以下代码进行联合，那么如何将这个用于union all？

List<tbEmployee> lstTbEmployee = obj.tbEmployees.ToList(); 
List<tbEmployee2> lstTbEmployee2 = (from a in lstTbEmployee 
            select new tbEmployee2 
            { 
             eid = a.eid, 
             ename = a.ename, 
             age = a.age, 
             dept = a.dept, 
             doj = a.doj, 
             dor = a.dor 

            }).Union(obj.tbEmployee2s).ToList(); 

Answer 1

Concat是SQL中UNION ALL的LINQ等效项。

我在LINQPad中设置了一个简单的例子来演示如何使用Union和Concat。如果你没有LINQPad，就明白吧。

为了能够看到这些设置操作的不同结果，第一组和第二组数据必须至少有一些重叠。在下面的例子中，两组都包含单词“不”。

打开LINQPad并将语言下拉菜单设置为C＃语句。以下内容粘贴到查询窗格中并运行它：

string[] jedi = { "These", "are", "not" }; 
string[] mindtrick = { "not", "the", "droids..." }; 

// Union of jedi with mindtrick 
var union = 
    (from word in jedi select word).Union 
    (from word in mindtrick select word); 

// Print each word in union 
union.Dump("Union"); 
// Result: (Note that "not" only appears once) 
// These are not the droids... 

// Concat of jedi with mindtrick (equivalent of UNION ALL) 
var unionAll = 
    (from word in jedi select word).Concat 
    (from word in mindtrick select word); 

// Print each word in unionAll 
unionAll.Dump("Concat"); 
// Result: (Note that "not" appears twice; once from each dataset) 
// These are not not the droids... 

// Note that union is the equivalent of .Concat.Distinct 
var concatDistinct = 
    (from word in jedi select word).Concat 
    (from word in mindtrick select word).Distinct(); 

// Print each word in concatDistinct 
concatDistinct.Dump("Concat.Distinct"); 
// Result: (same as Union; "not" only appears once) 
// These are not the droids... 

在LinqPad结果看起来是这样的：