Generate an unique random number followed by current date using C# and SQL Query in ASP.Net

Hi Hk110689,

I have created sample that full-fill your requirement.

HTML

<div>
    <asp:TextBox ID="txtDate" runat="server" />
    <br />
    <asp:Button ID="btnSubmit" Text="Submit" OnClick="Submit" runat="server" />
</div>

C#

protected void Submit(object sender, EventArgs e)
{
    string date = DateTime.Now.ToString("yyyyMMdd");
    int number = GetLastUniqueNumber();
    txtDate.Text = string.Format("{0}{1}", date, (number + 1).ToString().PadLeft(6, '0'));
}

private int GetLastUniqueNumber()
{
    int uniqueId;
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(@"DECLARE @CurrentDate VARCHAR(20)
                                                SET @CurrentDate = REPLACE(CONVERT(VARCHAR,GETDATE(),102),'.','')
                                                SELECT ISNULL(MAX(CAST(SUBSTRING(Id,9,DATALENGTH(Id)) AS INT)),0) FROM StudentsData WHERE SUBSTRING(Id,1,8) = @CurrentDate", con))
        {
            cmd.Connection.Open();
            uniqueId = Convert.ToInt32(cmd.ExecuteScalar());
            cmd.Connection.Close();
        }
    }
    return uniqueId;
}

Hope this works for you