多表连接时，where多条件对查询出的结果造成乱序影响？

select DATE_FORMAT(a.click_date,'%d') days,ifnull(b.count,0) as count
from (
    SELECT date_sub(curdate(), interval 1 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 2 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 3 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 4 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 5 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 6 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 7 day) as click_date
) a left join (
SELECT
    date(create_time) datetime,
    count(*) count
FROM t_video 
WHERE DATE_SUB( date_sub(curdate(), interval 1 day), INTERVAL 7 DAY ) <= date(create_time) 
GROUP BY datetime
) b on a.click_date = b.datetime;

以上是单个where过滤条件的SQL和结果，这样的一个结果顺序是我想要的（因为是日期，今天起过去的一周内的统计），但是我多加一个过滤条件就出现了乱序问题了，不理解下面这样是什么原因。

select DATE_FORMAT(a.click_date,'%d') days,ifnull(b.count,0) as count
from (
    SELECT date_sub(curdate(), interval 1 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 2 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 3 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 4 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 5 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 6 day) as click_date
    union all
    SELECT date_sub(curdate(), interval 7 day) as click_date
) a left join (
SELECT
    date(create_time) datetime,
    count(*) count
FROM t_video 
WHERE DATE_SUB( date_sub(curdate(), interval 1 day), INTERVAL 7 DAY ) <= date(create_time) 
    and category_id = (select id from t_category where category_name ='考证')
GROUP BY datetime
) b on a.click_date = b.datetime;

请求支援！感谢

你最外层加个排序就行了 order by days asc

你都没加任何排序（oeder by），完全是任由数据库自身默认的排序（数据库默认的排序你是猜不透猜不完的），所以查询会随着条件和数据的变化千变万化，写sql很基本的一个东西就是声明排序，即用order by，给个建议：除了声明order by 你要的字段排序后最好id主键也在排序中，这是一种最低保证排序（因为排序的字段可能也会完全相同，但id主键却绝不相同，特别是排序字段几条数据刚好都一样然后又没加id排序，分页的时候很容易出问题，如可能第一页和第二页好多数据是重复的）