This blog shows that how can we show the data of sql table in textboxes by just typing the id in one textbox__

Code : Type this code on the button_click event

string productCode;
productCode = textBox1.Text;
// You have to give the textbox where you enter the ID
SqlCommand cmd = cn.CreateCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = "select * from ProductDetails where ProductId=@Pode";

// Here ProductDetails is table name and ProductId is column name

cmd.Parameters.Add(new SqlParameter("@Pode", productCode));
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
textBox2.Text = Convert.ToString((dr[1]));
textBox3.Text = Convert.ToString((dr[2]));

//you can take more textboxes as per your table records

}

Thanks

Nikhil Kumar