Check if the Excel entries has duplicate in upload asp.net webform

Hi @Tuhin Paul, Thank you for your response however I have a question where did you get the Table[0] in DataTable dt = xl.ExcelData.Tables[0];

 an example of how you can modify your uploadfile1() method to check for duplicates:
 

 private bool uploadfile1()
{
    try
    {
        if (FileUpload1.PostedFile.FileName != "" || FileUpload1.PostedFile.FileName != "File Template")
        {
            this.checkDirectory();
            FileUpload1.PostedFile.SaveAs(Server.MapPath("") + "\\Uploads\\" + FileUpload1.FileName);
            filename = FileUpload1.FileName;
            path = Server.MapPath("") + "\\Uploads\\";
            ExcelCS xl = new ExcelCS();
            xl.UserId = (Session["userid"] != null) ? Session["userid"].ToString() : String.Empty;
            xl.Session = (Session["sessionID"] != null) ? Session["sessionID"].ToString() : String.Empty;
            if (xl.ParseExcelFile(path + filename, true, 1))
            {
                listdata save = new listdata();
                DataTable dt = xl.ExcelData.Tables[0]; // Get the first worksheet in the Excel file
                HashSet uniqueValues = new HashSet(); // Create a hash set to store the unique values
                foreach (DataRow row in dt.Rows)
                {
                    string value = row["ColumnName"].ToString(); // Replace "ColumnName" with the actual name of the column that contains the unique values
                    if (!uniqueValues.Contains(value)) // Check if the hash set already contains the value
                    {
                        uniqueValues.Add(value); // Add the value to the hash set if it's unique
                        // Add code to save the row to the SQL database here
                    }
                }
                // Add code to display the upload summary and refresh the page here
                return true;
            }
            else
            {
                Class.JSclass.ShowAlert("Invalid file format please use specified template.");
                listweb.Class.Logger.writeLog(Session["userid"].ToString(), Session["sessionID"].ToString(), "frmUploadFile.uploadfile1.ParseExcelFile", "Error: " + xl.Message, "", "", Class.LogCategories.SELECT);
                return false;
            }
        }
    }

Before iterating over the Excel rows, retrieve the primary key column name of the table where you will be storing the data. This can typically be found in the connection string or determined programmatically based on the table structure. Loop through each row in the Excel sheet, extract the data into variables, and then query the database to see if there already exists a record with the same value for the primary key column. If so, skip processing that row. Otherwise, insert the row into the database as usual.

To avoid duplicates when uploading Excel files in your ASP.NET C# web forms application, you should first check if the uploaded file contains duplicate rows before saving them in SQL. One way to do this is by adding a loop to iterate over each row in the Excel worksheet and comparing its values against existing records in the database.