实用编程技巧：MybatisPlus 结合 groupby 实现分组和 sum 求和

2023-12-09
广东
本文字数：1450 字
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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")@Datapublic 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;}

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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;   }

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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  }]

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🎈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")@Datapublic 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;}

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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;   }

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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  }]