CREATE TABLE `merchant_purchase_stat` ( `id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT, `merchant_id` BIGINT UNSIGNED DEFAULT NULL COMMENT '商户ID，关联merchant主键', `goods_model` VARCHAR ( 300 ) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '基本库商品型号ID', `num` INT NOT NULL DEFAULT '0' COMMENT '数量', `stat_type` INT NOT NULL DEFAULT '0' COMMENT '统计类型，1、购买量 2、增长幅度', `market_date` date NOT NULL COMMENT '基本库商品上市时间（首发时间）', `stat_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '统计时间', PRIMARY KEY ( `id` ) USING BTREE, KEY `idx_merchant_id` ( `merchant_id` ) USING BTREE, KEY `idx_goods_model` ( `goods_model` ) USING BTREE ) ENGINE = INNODB DEFAULT CHARSET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = DYNAMIC COMMENT = '店铺采购统计';根据表结构生成java实体类，持久层，业务层，添加注释，以及crud

根据表结构生成java实体类、持久层和业务层，添加注释以及CRUD操作的步骤如下：

1. 创建Java实体类MerchantPurchaseStat，包含以下属性：

   public class MerchantPurchaseStat {
       private Long id;
       private Long merchantId;
       private String goodsModel;
       private Integer num;
       private Integer statType;
       private LocalDate marketDate;
       private LocalDateTime statTime;
       // getter and setter methods
   }

2. 创建持久层接口MerchantPurchaseStatMapper，使用MyBatis框架进行数据访问：

   @Mapper
   public interface MerchantPurchaseStatMapper {
       void insert(MerchantPurchaseStat stat);
       void update(MerchantPurchaseStat stat);
       void deleteById(Long id);
       MerchantPurchaseStat findById(Long id);
       List<MerchantPurchaseStat> findByMerchantId(Long merchantId);
       List<MerchantPurchaseStat> findByGoodsModel(String goodsModel);
       List<MerchantPurchaseStat> findByMarketDate(LocalDate marketDate);
   }

3. 创建业务层接口MerchantPurchaseStatService，定义CRUD操作方法：

   public interface MerchantPurchaseStatService {
       void create(MerchantPurchaseStat stat);
       void update(MerchantPurchaseStat stat);
       void deleteById(Long id);
       MerchantPurchaseStat findById(Long id);
       List<MerchantPurchaseStat> findByMerchantId(Long merchantId);
       List<MerchantPurchaseStat> findByGoodsModel(String goodsModel);
       List<MerchantPurchaseStat> findByMarketDate(LocalDate marketDate);
   }

4. 实现业务层接口MerchantPurchaseStatServiceImpl，调用持久层接口方法实现CRUD操作：

   @Service
   public class MerchantPurchaseStatServiceImpl implements MerchantPurchaseStatService {
       @Autowired
       private MerchantPurchaseStatMapper mapper;
       
       @Override
       public void create(MerchantPurchaseStat stat) {
           mapper.insert(stat);
       }
       
       @Override
       public void update(MerchantPurchaseStat stat) {
           mapper.update(stat);
       }
       
       @Override
       public void deleteById(Long id) {
           mapper.deleteById(id);
       }
       
       @Override
       public MerchantPurchaseStat findById(Long id) {
           return mapper.findById(id);
       }
       
       @Override
       public List<MerchantPurchaseStat> findByMerchantId(Long merchantId) {
           return mapper.findByMerchantId(merchantId);
       }
       
       @Override
       public List<MerchantPurchaseStat> findByGoodsModel(String goodsModel) {
           return mapper.findByGoodsModel(goodsModel);
       }
       
       @Override
       public List<MerchantPurchaseStat> findByMarketDate(LocalDate marketDate) {
           return mapper.findByMarketDate(marketDate);
       }
   }

5. 在实体类和持久层接口中添加注释，描述类和方法的作用。

6. 在数据库中使用CRUD操作测试持久层和业务层的功能是否正常。