c# - SQLクエリと同等のLINQのケースクエリ

Question

呼び出し元、呼び出し先フィールドを含むデータセットがあり、このSQLクエリと同等のこのデータセットを操作するにはLINQクエリが必要です

SELECT CASE
     WHEN caller < callee THEN callee
     ELSE caller
   END      AS caller1,
   CASE
     WHEN caller < callee THEN caller
     ELSE callee
   END      AS caller2,
   Count(*) AS [Count]
    FROM   YourTable
   GROUP  BY CASE
        WHEN caller < callee THEN callee
        ELSE caller
      END,
      CASE
        WHEN caller < callee THEN caller
        ELSE callee
      END 

Answer 1

これはあなたが求めているものですか？

DataSet dataSet = new DataSet();
DataTable dataTable = new DataTable("dataTable");

dataTable.Columns.Add("caller", typeof(String));
dataTable.Columns.Add("callee", typeof(String));

dataTable.Rows.Add("999", "888");
dataTable.Rows.Add("888", "999");
dataTable.Rows.Add("999", "555");
dataTable.Rows.Add("555", "333");
dataTable.Rows.Add("555", "999");

dataSet.Tables.Add(dataTable);

string filter = "999";

var result = dataSet.Tables["dataTable"].Select().Select(dr =>
    new
    {
        caller1 = StringComparer.CurrentCultureIgnoreCase.Compare(dr["caller"], dr["callee"]) < 0 ? dr["callee"] : dr["caller"],
        caller2 = StringComparer.CurrentCultureIgnoreCase.Compare(dr["caller"], dr["callee"]) < 0 ? dr["caller"] : dr["callee"]
    })
        .Where(dr => String.IsNullOrEmpty(filter) || dr.caller1 == filter || dr.caller2 == filter)
        .GroupBy(drg => new { drg.caller1, drg.caller2 } )
        .Select(drg => new { drg.Key.caller1, drg.Key.caller2, count = drg.Count() });

Answer 2

これが探しているものです。case ステートメントを再利用して LINQ クエリを簡素化するのに役立つ範囲変数の使用に注意してください。

var query = from y in YourTable
            //place the result of the case statement into a range variable so we can reuse it for the grouping
            let caller1 = y.caller < y.callee ? y.callee : y.caller
            let caller2 = y.caller < y.callee ? y.caller : y.callee
            //group the results
            group y by new { caller1, caller2 } into grouping
            select new
            {            
                //get the range variables from the grouping key
                grouping.Key.caller1,
                grouping.Key.caller2,
                //get the count of the grouping
                Count = grouping.Count(),
            };

Answer 3

SELECT CASE
  WHEN caller < callee THEN callee
  ELSE caller
END      AS caller1

に翻訳されます

caller1 = x.caller < x.callee ? x.callee : x.caller