实用编程技巧：MybatisPlus结合groupby实现分组和sum求和

知识浅谈

发布于 2023-12-09 10:35:22

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✅MybatisPlus结合groupby实现分组和sum求和这次使用的是LambdaQueryWrapper，使用QueryWrapper相对来说简单点就不写了

🎈实现GroupBy分组

第一步: 实体类中新增一个字段count

@TableName(value ="user")
@Data
public class User implements Serializable {
    @TableId(type = IdType.AUTO)
    private Integer id;

    @TableField(value = "name")
    private String name;

    @TableField(value = "age")
    private Integer age;

    @TableField(value = "state")
    private String state;

    @TableField(exist = false)
    private static final long serialVersionUID = 1L;
	
	//这个地方
    @TableField(value = "count(*)",insertStrategy = FieldStrategy.NEVER,updateStrategy = FieldStrategy.NEVER)
    private  Integer count;
}

第二步：查询接口中修改

   @GetMapping("/count")
   public List<User> count(){
       new QueryWrapper<>()
       LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
       queryWrapper.select(User::getState,User::getCount);
       queryWrapper.groupBy(User::getState);
       List<User> list = userService.list(queryWrapper);
       return list;
   }

返回的结果

[
  {
    "id": null,
    "name": null,
    "age": null,
    "state": "1",
    "count": 3
  },
  {
    "id": null,
    "name": null,
    "age": null,
    "state": "2",
    "count": 2
  }
]

🎈实现GroupBy分组之后再sum求和

第一步: 实体类中新增一个字段count

@TableName(value ="user")
@Data
public class User implements Serializable {
    @TableId(type = IdType.AUTO)
    private Integer id;

    @TableField(value = "name")
    private String name;

    @TableField(value = "age")
    private Integer age;

    @TableField(value = "state")
    private String state;

    @TableField(exist = false)
    private static final long serialVersionUID = 1L;
	
    @TableField(value = "count(*)",insertStrategy = FieldStrategy.NEVER,updateStrategy = FieldStrategy.NEVER)
    private  Integer count;

	//这个地方
    @TableField(value = "sum(age)",insertStrategy = FieldStrategy.NEVER,updateStrategy = FieldStrategy.NEVER)
    private  Integer ages;
}

第二步：查询接口中修改

   @GetMapping("/count")
   public List<User> count(){
       new QueryWrapper<>()
       LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
       //这个地方新增了一个字段
       queryWrapper.select(User::getState,User::getCount,User::getAges);
       queryWrapper.groupBy(User::getState);
       List<User> list = userService.list(queryWrapper);
       return list;
   }

返回的结果

[
  {
    "id": null,
    "name": null,
    "age": null,
    "state": "1",
    "count": 3,
    "ages": 6
  },
  {
    "id": null,
    "name": null,
    "age": null,
    "state": "2",
    "count": 2,
    "ages": 9
  }
]