Making compute column in ado.net with conditions

A question came up in the My Mind as to how to handle Data Column Expressions within a DataTable in Ado.Net. The expression syntax available to create calculated columns is probably much richer than you might think if you don't play around a lot with the Expression Property of the DataColumn.
The question was how to create a Calculated ColumnC that had the following logic:
  • If ColumnA - ColumnB > 100, ColumnC = “Yes“, else ColumnC = “No“
We can create a DataTable to do this in only a few lines of code:
      
   
   // Create the DataTable
    DataTable dt = new DataTable("Expressions");

    // Create PriceA and PriceB
    DataColumn PriceA = new DataColumn("ValueA", typeof(int));
    DataColumn PriceB = new DataColumn("ValueB", typeof(int));
    dt.Columns.AddRange(new DataColumn[] { PriceA, PriceB });

    // Add a Couple of Rows Supplying PriceA and PriceB Data...
    dt.Rows.Add(new object[] { 200, 50 });
    dt.Rows.Add(new object[] { 100, 20 });
    dt.Rows.Add(new object[] { 30, 80 });
    dt.Rows.Add(new object[] { 50, 170 });

   
    // Create Compute column
    DataColumn dtAvg =  new DataColumn("Average", typeof(float),
            "(PriceA + PriceB) /2");
    dt.Columns.Add(dtAvg);

    // Create Compute column with Condition
    DataColumn dtIsGAvg = new DataColumn("IsGoodAvg", typeof(string),"IIF(Average > 100,'Yes','No')");
    dt.Columns.Add(dtIsGAvg);



    grd.DataSource = dt;
    grd.DataBind();


Or when we connect from the back end sql server and filling data table from some of the table like givien bellow tblOrder then how to make compute column for getting average of column and and for calulate the average is greater than 100 or not. 



string sqlConStr = "Data Source=.; Initial Catalog=MyDatabase; Integrated   security=true;";
    string sqlSelect = "SELECT PriceA,PriceB FROM tblOrder";

    SqlDataAdapter da = new SqlDataAdapter(sqlSelect, sqlConStr);
    DataTable dt = new DataTable();
    da.Fill(dt);

     
    // Create Compute column
    DataColumn dtAvg = new DataColumn("Average", typeof(float),
            "(PriceA + PriceB) /2");
    dt.Columns.Add(dtAvg);

    // Create Compute column with Condition
    DataColumn dtIsGAvg = new DataColumn("IsGoodAvg", typeof(string),"IIF(Average > 100,'Yes','No')");
    dt.Columns.Add(dtIsGAvg);

    grd.DataSource = dt;
    grd.DataBind();


As you can see above, there is an IIF Function available to us that populates the column based on whether an expression is true or false.

   IIF(expr, truepart, falsepart) 
  • expr -- The expression to evaluate.
  • truepart -- The value to return if the expression is true.
  • falsepart -- The value to return if the expression is false.
I wrote the expression as follows:
IIF(Average > 100,'Yes','No')

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