SQL用户存在则更新不存在则删除

      alter table T_Cart add unique index(goods_id,user_id);


    

      /*

	 * 保存购物车(如果不存在则插入,如果存在则更新)

	 */

	@Override

	public void insetCart(Cart cart) throws Exception {

		String sql = "INSERT INTO T_Cart(goods_id,order_num,user_id) VALUES(?,?,?) ON DUPLICATE KEY UPDATE order_num=order_num+?";

		util.update(sql, cart.getGoods_id(),cart.getOrder_num(), cart.getUser_id(),cart.getOrder_num());

	}