MySQL 从小时 :minute format 获取日期

Question

对于 where 子句，如果我有一个 %h:%i 字符串，我怎样才能在 now() 与那个小时/分钟组合？

一些虚构的 select 来显示预期的行为(comb 是我需要的神奇函数/组合器，它可以显式依赖于 now() 或不):

mysql> select now(), comb('20:20');
+---------------------+---------------------+
| now()               | comb('20:20')       |
+---------------------+---------------------+
| 2016-11-12 20:43:39 | 2016-11-12 20:20:00 |
+---------------------+---------------------+

mysql> select now(), comb('20:20');
+---------------------+---------------------+
| now()               | comb('20:20')       |
+---------------------+---------------------+
| 2016-11-11 01:43:39 | 2016-11-10 20:20:00 |
+---------------------+---------------------+

mysql> select now(), comb('20:20');
+---------------------+---------------------+
| now()               | comb('20:20')       |
+---------------------+---------------------+
| 2016-01-01 01:43:39 | 2015-12-31 20:20:00 |
+---------------------+---------------------+

Answer 1

select concat(date(if(time(now()) > '20:20', now(), date_sub(now(), INTERVAL 1 day))), ' 20:20');