//tables that will be merged

DataTable table1 = new DataTable();

DataTable table2 = new DataTable(); //duplicates will be removed

//columns used to store what is found in the row's column

string column1 = string.Empty; 

string column2 = string.Empty;

// loop through the rows in the first table and if

// the columns are found on an item in the second

//table then remove it

foreach (DataRow row in table1.Rows)

{

    //set the column variables to what is in the 

    //current row

    column1 = row["column 1 Name"].ToString();

    column2 = row["column 2 Name"].ToString();

    //get an array of each of the rows that match

    //the columns in the current row

    DataRow[] duplicateRows = table2.Select("Section = '" + 

        column1 + "' AND Subsection = '" + column2 + "'");

    //loop through and remove each of the rows in the 

    //table that are duplicates 

    foreach (DataRow duplicateRow in duplicateRows)

        table2.Rows.Remove(duplicateRow);

}

//merge the tables so that we now have 1

table1.Merge(table2);