C#

MyDataAdapter.Fill(MyDataTable);
MyMasterDGV.DataSource = myDataTable;
MyDetailDGV.DataSource = myDataTable;

private string connectionString = "Data Source=DESKTOP-5GRDQ7C\\SQLEXPRESS;Initial Catalog=Orders;Integrated Security=True"; 
        private SqlDataAdapter masterDataAdapter;
        private SqlDataAdapter detailDataAdapter;
        private DataSet dataSet;

        public Form1()
        {
            InitializeComponent();
        }

        
        private void LoadMasterData()
        {
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                string query = "SELECT * FROM ordm";
                SqlDataAdapter adapter = new SqlDataAdapter(query, connection);
                DataTable dataTable = new DataTable();
                adapter.Fill(dataTable);

               
                masterDataGridView.DataSource = dataTable;
            }
        }
        private void LoadData()
        {
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
           
                string ordmQuery = "SELECT * FROM ORDM";
                masterDataAdapter = new SqlDataAdapter(ordmQuery, connection);
                masterDataAdapter.Fill(dataSet, "ORDM");

              
                string ordcQuery = "SELECT * FROM ORDC";
                detailDataAdapter = new SqlDataAdapter(ordcQuery, connection);
                detailDataAdapter.Fill(dataSet, "ORDC");
            }

            
            DataColumn parentColumn = dataSet.Tables["ORDM"].Columns["ORD_NO"];
            DataColumn childColumn = dataSet.Tables["ORDC"].Columns["ORD_NO"];
            DataRelation relation = new DataRelation("ORDM_ORDC_Relation", parentColumn, childColumn);
            dataSet.Relations.Add(relation);
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            LoadMasterData();
           
            dataSet = new DataSet();
            LoadData();

           
            masterDataGridView.DataSource = dataSet.Tables["ORDM"];

            
            masterDataGridView.SelectionChanged += masterDataGridView_SelectionChanged_1;
        }

        private void masterDataGridView_SelectionChanged_1(object sender, EventArgs e)
        {
           
            if (masterDataGridView.SelectedRows.Count > 0)
            {
              
                string orderNumber = Convert.ToString(masterDataGridView.SelectedRows[0].Cells["ordcol"].Value);

              
                LoadChildData(orderNumber);
            }
        }
            private void LoadChildData(string orderNumber)
            {
                using (SqlConnection connection = new SqlConnection(connectionString))
                {
                   
                    string query = $"SELECT * FROM ordc WHERE ord_no = ord_no";
                    SqlDataAdapter adapter = new SqlDataAdapter(query, connection);
                    DataTable dataTable = new DataTable();
                    adapter.Fill(dataTable);

                   
                    childDataGridView.DataSource = dataTable;
                }
            }
    }

string query = $"SELECT * FROM ordc WHERE ord_no = ord_no";