C#

public static DataTable GetAll()
{
    using DataTable dt = new();
    try
    {
        string query = "
                        select
                            l.LineID,
                            s.SheetID,
                            z.ZoneID,
                            j.JointTypeID,
                            j.JointClassID ,
                            j.PipeClassID ,
                            j.HoldID,
                            l.[LineNo] ,
                            s.Sheet,
                            s.Rev ,
                            s.RevIndex ,
                            z.Unit,
                            z.Area,
                            s.SheetStatus as LineStatus,
                            j.JointID,
                            j.JointNo ,
                            j.JointIndex ,
                            j.JointStatus ,
                            cast(CAST(j.JointSize as decimal(18,2)) as float) as JointSize,
                            j.[Location],
                            j.Spool,
                            jt.JointType,
                            jc.JointClassName as Class,
                            pc.PipeClass,
                            m.MaterialName as Mat,
                            j.Thk
                        from
                        Joint  as j
                        inner join Sheet as s on s.SheetID = j.SheetID and s.VoidDate is null
                        inner join  Line as l on l.LineID=s.LineID
                        left join Zone as z on z.ZoneID = j.ZoneID
                        left join JointType as jt on jt.JointTypeID = j.JointTypeID
                        left join JointClass as jc on jc.JointClassID = j.JointClassID
                        left join PipingClass as pc on pc.PipeClassID = j.PipeClassID
                        left join Material as m on m.MaterialID = pc.MaterialID
                        left join MTO as m1 on m1.SheetID = j.SheetID AND m1.PTNo = Mat1
                        left join MTO as m2 on m2.SheetID = j.SheetID AND m2.PTNo = Mat2
                        ";
        using SqlCommand cmd = new SqlCommand(query, Connection.Conn);
        Connection.Open();
        using SqlDataReader rd = cmd.ExecuteReader();
        dt.Load(rd);

    }
    catch (SqlException ex)
    {
        Error = ex.Message;
    }
    finally
    {
        Connection.Close();
    }
    return dt;
}

public static DataTable GetAll()
      {
          return JointDAL.GetAll();
      }

DG_Joint.DataSource = JointBLL.GetAll();

I don't know if I wrote it explicitly or not, but what I mean by creating this topic is to review the multi-layer program, what codes should be written in each layer.