mysql日期分组，无数据的行数据返回0

-- 创建表结构
DROP TABLE IF EXISTS `group_test`;
create table group_test
(
    id          varchar(36)  not null primary key,
    name        varchar(128) not null comment 'name',
    count       int       default 0 comment 'count',
    create_time timestamp default CURRENT_TIMESTAMP comment 'createTime'
) comment '分组测试';

-- 造数据
insert into group_test
values (1, 'name1', round(rand()*100), now() - interval 1 month);
insert into group_test
values (2, 'name2', round(rand()*100), now() - interval 2 month);
insert into group_test
values (3, 'name3', round(rand()*100), now() - interval 3 month);
insert into group_test
values (4, 'name4', round(rand()*100), now() - interval 4 month);
insert into group_test
values (5, 'name5', round(rand()*100), now() - interval 5 month);
insert into group_test
values (6, 'name6', round(rand()*100), now() - interval 6 month);
insert into group_test
values (7, 'name7', round(rand()*100), now() - interval 7 month);
insert into group_test
values (8, 'name8', round(rand()*100), now() - interval 8 month);
insert into group_test
values (9, 'name9', round(rand()*100), now() - interval 9 month);

-- 查询sql，这里将会查询最近六个月的数据，并且计算得出每个月的总和
select concat(date_format(date,'%m'),'月') as month, ifnull(sum(b.count), 0) as sum
from (SELECT LAST_DAY(CURRENT_DATE) + INTERVAL 1 DAY - INTERVAL 1 MONTH AS date
      UNION ALL
      SELECT LAST_DAY(CURRENT_DATE) + INTERVAL 1 DAY - INTERVAL 2 MONTH
      UNION ALL
      SELECT LAST_DAY(CURRENT_DATE) + INTERVAL 1 DAY - INTERVAL 3 MONTH
      UNION ALL
      SELECT LAST_DAY(CURRENT_DATE) + INTERVAL 1 DAY - INTERVAL 4 MONTH
      UNION ALL
      SELECT LAST_DAY(CURRENT_DATE) + INTERVAL 1 DAY - INTERVAL 5 MONTH
      UNION ALL
      SELECT LAST_DAY(CURRENT_DATE) + INTERVAL 1 DAY - INTERVAL 6 MONTH) a
         left join
     group_test b on a.date = LAST_DAY(b.create_time) + INTERVAL 1 DAY - INTERVAL 1 MONTH
group by a.date

在解决该问题的过程中，发现date_sub()，date_add() 可以使用运算符'+'，'-'进行替换，
但是在使用时并不放心是否是优雅的使用方式，于是查询了 mysql8.0参考手册 ，并且
在文档中找到相关的介绍，文档中明确的表示是可以使用运算符进行替换的。