关于c#中DataTable的Select过滤

Posted 2023-04-24

dtTrees中的数据为select a.* from tb a，目标实现查询语句select a.* from tb a where exists (select 1 from tb b where a.id=b.pid)，现没办法改变dtTrees数据源查询，请问如何在dtTrees.Select(exists (select 1 from tb b where a.id=b.pid))中实现如此过滤查询？
比如实现：
表结构如下（数据是动态的）：
id pid name
28 27 a1
29 28 a2
30 28 a3
31 27 a4
32 31 a5
33 31 a6

要求查询结果：
id pid name
28 27 a1
31 27 a4

参考技术A string a = ""; //这里可以使用StringBuilder
foreach (DataRow dr in dtTrees.Rows)

a += dr[0].ToString() + ",";

a = a.Trim(',');
DataRow[] drs = dtTrees.Select("pid not in (" + a + ")"); //这里用not in
//drs就是所要的查询结果。本回答被提问者和网友采纳 参考技术B 把select 1 from tb b where a.id=b.pid中的id以逗号分隔,弄成一个字符串,然后dtTrees.Select(id exists(弄成的字符串)) 参考技术C dtTrees.Select( "id = pid"); 参考技术D 不懂你要过滤什么

DataTable通过Select进行过滤

DataTable方法测试

  //测试DataTable的select
            DataTable dt = new DataTable();
            //a.OrderType,
            //a.[Status]
            dt.Columns.Add("No", typeof(String));
            dt.Columns.Add("Type", typeof(String));
            dt.Columns.Add("Status", typeof(String));

            dt.Rows.Add(new object[]  "A01", "N", "N1" );
            dt.Rows.Add(new object[]  "A01", "G", "G1" );
            dt.Rows.Add(new object[]  "A01", "T", "T1" );
            dt.Rows.Add(new object[]  "A01", "N", "N2" );
            dt.Rows.Add(new object[]  "A02", "G", "G1" );
            dt.Rows.Add(new object[]  "A02", "T", "T1" );
            dt.Rows.Add(new object[]  "A03", "N", "N1" );
            dt.Rows.Add(new object[]  "A04", "S", "S1" );
            dt.Rows.Add(new object[]  "A05", "G", "G1" );
            dt.Rows.Add(new object[]  "A05", "T", "T1" );

            DataRow[] arrRow = dt.Select("No=‘A01‘ and ((Type=‘N‘) or (Type=‘G‘ and Status<>‘G1‘) or(Type=‘T‘ and Status<>‘T1‘))");
            //Console.WriteLine(arrRow[0]["Type"]);
         
           var arrRow2= arrRow.Select<DataRow,DataRow>(dr=> 
                if (dr["Type"].ToString() == "N")
                    return dr;
                else
                   return null;
            );
            foreach(var r in arrRow2)
            
                if(r!=null)
                    Console.WriteLine(r["No"].ToString()+"===="+r["Status"].ToString());