LambdaQueryWapper与QueryWapper的一些特殊用法

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QueryWrapper的group by方法

        QueryWrapper queryWrapper=new QueryWrapper();
        queryWrapper.select("dept_id,count(1) countSum");
        queryWrapper.groupBy("dept_id");
        queryWrapper.isNotNull("dept_id");

LambdaQueryWapper的group by方法

        lambdaQueryWrapper.select(AdminUserDO::getDeptId,Functions.max(AdminUserDO::salary)).groupBy(AdminUserDO::getDeptId).isNotNull(AdminUserDO::getDeptId);

这个方式是在其他网站看到的，有个问题，没有找到Functions.max这个方法

LambdaQueryWapper的多表连接查询

MPJLambdaWrapper< UserDO > wrapper = new MPJLambdaWrapper<UserDO>()
        .selectAll(UserDO.class)
        .select(UserDetailDO::getTel)
        .selectAs(UserDetailDO::getAddress, UserDTO::getUserAddress)
        .leftJoin(UserDetailDO.class, UserDetailDO::getUserId, UserDO::getId)
        .eq(UserDO::getSex, 1)
        .like(UserDetailDO::getAddress, "海淀")
 
//列表查询
List<UserDTO> list = userMapper.selectJoinList(UserDTO.class, wrapper);
 
//分页查询 （需要启用 mybatis plus 分页插件）
List<UserDTO> listPage = userMapper.selectJoinPage(new Page<>(1, 10), UserDTO.class, wrapper);

生成的sql是这样的（未验证）

SELECT 
    u.id,
    u.name,
    u.sex,
    u.head_img,
    ud.tel,
    ud.address AS user_address
FROM 
    user u
    LEFT JOIN user_detail ud on u.id = ud.user_id
WHERE u.sex = 1 AND ud.address LIKE "%海淀%"