public String buy(Long goodsId, Integer goodsNum) {
    //查詢商品庫存
    Goods goods = goodsMapper.selectById(goodsId);
    //如果當(dāng)前庫存為0，提示商品已經(jīng)賣光了
    if (goods.getGoodsInventory() <= 0) {
        return "商品已經(jīng)賣光了！";
    }
    //如果當(dāng)前購買數(shù)量大于庫存，提示庫存不足
    if (goodsNum > goods.getGoodsInventory()) {
        return "庫存不足！";
    }
    //更新庫存
    goods.setGoodsInventory(goods.getGoodsInventory() - goodsNum);
    goodsMapper.updateById(goods);
    return "購買成功！";
}

CREATE TABLE `t_goods` (
  `id` bigint NOT NULL COMMENT '物理主鍵',
  `goods_name` varchar(64) DEFAULT NULL COMMENT '商品名稱',
  `goods_pic` varchar(255) DEFAULT NULL COMMENT '商品圖片',
  `goods_desc` varchar(255) DEFAULT NULL COMMENT '商品描述信息',
  `goods_inventory` int DEFAULT NULL COMMENT '商品庫存',
  `goods_price` decimal(10,2) DEFAULT NULL COMMENT '商品價格',
  `create_time` datetime DEFAULT NULL COMMENT '創(chuàng)建時間',
  `update_time` datetime DEFAULT NULL COMMENT '更新時間',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

<!--使用redisson作為分布式鎖-->
<dependency>
    <groupId>org.redisson</groupId>
    <artifactId>redisson</artifactId>
    <version>3.16.8</version>
</dependency>

import org.redisson.Redisson;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class RedissonConfig {
    /**
     * 所有對Redisson的使用都是通過RedissonClient對象
     *
     * @return
     */
    @Bean(destroyMethod = "shutdown")
    public RedissonClient redissonClient() {
        // 創(chuàng)建配置 指定redis地址及節(jié)點信息
        Config config = new Config();
        config.useSingleServer().setAddress("redis://127.0.0.1:6379").setPassword("123456");
        // 根據(jù)config創(chuàng)建出RedissonClient實例
        RedissonClient redissonClient = Redisson.create(config);
        return redissonClient;
    }
}

public String buyRedisLock(Long goodsId, Integer goodsNum) {
    RLock lock = redissonClient.getLock("goods_buy");
    try {
        //加分布式鎖
        lock.lock();
        //查詢商品庫存
        Goods goods = goodsMapper.selectById(goodsId);
        //如果當(dāng)前庫存為0，提示商品已經(jīng)賣光了
        if (goods.getGoodsInventory() <= 0) {
                return "商品已經(jīng)賣光了！";
        }
        //如果當(dāng)前購買數(shù)量大于庫存，提示庫存不足
        if (goodsNum > goods.getGoodsInventory()) {
                return "庫存不足！";
        }
        //更新庫存
        goods.setGoodsInventory(goods.getGoodsInventory() - goodsNum);
        goodsMapper.updateById(goods);
        return "購買成功！";
    } catch (Exception e) {
        log.error("秒殺失敗");
    } finally {
        lock.unlock();
    }
    return "購買失敗";
}

//查詢商品庫存
Goods goods = goodsMapper.selectById(goodsId);
原始查詢SQL
SELECT *
  FROM t_goods
  WHERE id = #{goodsId}
改寫為
 SELECT *
  FROM t_goods
  WHERE id = #{goodsId} for update

`version` int(11) DEFAULT NULL COMMENT '版本'

update t_goods
set goods_inventory = goods_inventory - #{goodsNum},
     version         = version + 1
where id = #{goodsId}
and version = #{version}

public String buyVersion(Long goodsId, Integer goodsNum) {
    //查詢商品庫存(該語句使用了行鎖)
    Goods goods = goodsMapper.selectById(goodsId);
    //如果當(dāng)前庫存為0，提示商品已經(jīng)賣光了
    if (goods.getGoodsInventory() <= 0) {
        return "商品已經(jīng)賣光了！";
    }
    if (goodsMapper.updateInventoryAndVersion(goodsId, goodsNum, goods.getVersion()) > 0) {
      return "購買成功！";
    }
    return "庫存不足！";
}

//更新庫存
goods.setGoodsInventory(goods.getGoodsInventory() - goodsNum);
goodsMapper.updateById(goods);

update t_goods
 set goods_inventory = goods_inventory - #{goodsNum}
 where id = #{goodsId}

update t_goods
set goods_inventory = goods_inventory - #{goodsNum}
where id = #{goodsId}
AND (goods_inventory - #{goodsNum}) >= 0

public String buySqlUpdate(Long goodsId, Integer goodsNum) {
    //查詢商品庫存(該語句使用了行鎖)
    Goods goods = goodsMapper.queryById(goodsId);
    //如果當(dāng)前庫存為0，提示商品已經(jīng)賣光了
    if (goods.getGoodsInventory() <= 0) {
        return "商品已經(jīng)賣光了！";
    }
    //此處需要判斷更新操作是否成功
    if (goodsMapper.updateInventory(goodsId, goodsNum) > 0) {
        return "購買成功！";
     }
    return "庫存不足！";
}