SqlConnection Conn=....
//初始化,comboBox1绑定客户表
string Sql= "select customerName from customer";
DataSet Ds= new DataSet();
SqlDataAdapter Da= new SqlDataAdapter(Sql, Conn);
Da.Fill(Ds, "customer");
comboBox1.DataSource = Ds.Tables["customer"];
comboBox1.DisplayMember = "customerName";