How to Merge 3 DataTables into Single DataTable In C# Windows Application ?

i tried as below...it is showing only 3rd table data in crystal report..

private void btnViewCrystal_Click(object sender, EventArgs e)
{
DataSet1 ds = new DataSet1();

// Create First DataTable
DataTable t = ds.Tables.Add("EmpDetails");


t.Columns.Add("EmpNo", Type.GetType("System.Int32"));
// t.PrimaryKey = new[] { t.Columns["EmpNo"] };

t.Columns.Add("EmpName", Type.GetType("System.String"));
t.Columns.Add("DateOfBirth", Type.GetType("System.String"));
t.Columns.Add("Address", Type.GetType("System.String"));
t.Columns.Add("Country", Type.GetType("System.String"));
t.Columns.Add("DeptNo", Type.GetType("System.Int32"));
t.PrimaryKey = new DataColumn[] { t.Columns["DeptNo"] }; // Primary Key For DeptNo
DataRow r;

r = t.NewRow();
r["EmpNo"] = txtEmpNo.Text;
r["EmpName"] = txtName.Text;
r["DateOfBirth"] = txtDay.Text + " /" + txtMonth.Text + " /" + txtYear.Text;

r["Address"] = txtAddress.Text;
r["Country"] = txtCountry.Text;
r["DeptNo"] = txtDeptNo.Text;

t.Rows.Add(r);

// Create Second DataTable
OleDbConnection cn = new OleDbConnection(ConfigurationManager.ConnectionStrings["strConn"].ConnectionString);
cn.Open();
OleDbCommand cmd = new OleDbCommand();
OleDbDataAdapter da = new OleDbDataAdapter();
DataTable dt = new DataTable();
cmd.Connection = cn;

cmd.CommandText = "select * from tblDepartment Where DeptNo=@DeptNo";
cmd.Parameters.Add("DeptNo", OleDbType.Integer).Value = int.Parse(txtDeptNo.Text);

da.SelectCommand = cmd;

dt.Clear();
da.Fill(dt);
//ds.Tables.Add(dt);
t.Merge(dt, false, MissingSchemaAction.Add);
t.AcceptChanges();

//Create Third Table
DataTable ldt = ds.Tables.Add("LetterDetails");;
ldt.Columns.Add("DeptNo", Type.GetType("System.Int32"));
ldt.PrimaryKey = new DataColumn[] { ldt.Columns["DeptNo"] }; // Primary Key For DeptNo

ldt.Columns.Add("LId", Type.GetType("System.Int32"));
ldt.Columns.Add("Letters", Type.GetType("System.String"));

DataRow rl;

rl = ldt.NewRow();
rl["DeptNo"] = txtDeptNo.Text;
rl["LId"] = txtLId.Text;
rl["Letters"] = txtLetters.Text;
ldt.Rows.Add(rl);

t.Merge(ldt, false, MissingSchemaAction.Add);
t.AcceptChanges();
//To Show The CrystalReport1 In CrystalReportViewer
CrystalReport1 objRpt = new CrystalReport1();
objRpt.SetDataSource(ldt);

crystalReportViewer1.ReportSource = objRpt;
crystalReportViewer1.Refresh();


}