find duplicate records in a datatable using LINQ | Example to find duplicate values from datatable or dataset using Linq Query

hi in this post i will show to find duplicate records in a datatable or dataset using LINQ.

Example:

Below is the sample employee table which i will take it into a datatable and then will search for duplicate employee names present inside the table using a LINQ query.

1. EMP Table

Code :

 public void checkDuplicate()
    {
        string conStr = ConfigurationManager.ConnectionStrings["NORTHWNDConnectionString"].ConnectionString.ToString();
        StringBuilder s = new StringBuilder();
        SqlConnection s1 = new SqlConnection(conStr);
        s1.Open();

        string queryString = "SELECT * FROM employee";
        SqlDataAdapter adapter = new SqlDataAdapter(queryString, s1);

        DataSet employee = new DataSet();
        adapter.Fill(employee, "employee");

        var duplicateRecords = employee.Tables[0].AsEnumerable()
                 .GroupBy(r => r["EmpName"]) //coloumn name which has the duplicate values
                 .Where(gr => gr.Count() > 1)
                 .Select(g => g.Key);


        foreach (var d in duplicateRecords)
        {
           s.Append("," + d.ToString());
        }

         Response.Write("<script language='javascript'>alert('Duplicates Names: "+ s.ToString() +"');</script>");
         s1.Close();
        
    }

Output :

Output