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Form1 af = new Form1();

        public Add_Form()
        {
            string connectionString = "data source=localhost; initial catalog = owo; persist security info = True; Integrated Security = SSPI; ";
            string selectedTable = comboBox1.SelectedItem.ToString();
            string sql = $"SELECT * FROM [{selectedTable}] WHERE id < 0";
            InitializeComponent();
            af.RefreshTable();
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            string selectedTable = comboBox1.SelectedItem.ToString();
        }

        private void refresh_button_Click(object sender, EventArgs e)
        {

            af.RefreshTable();
        }