查询返回空行

Question

我有一个查询返回所有字段的空行，而不是返回0行。我认为Min是问题，一旦我删除它，它开始返回0行。如何在不改变查询结果的情况下修复它？

select *,min(STR_TO_DATE(concat(slot_date, ' ' , sec_to_time(from_time)),  '%Y-%m-%d %H:%i')) next_available_slot 
from  appt_available_slots 
where country_id = 1 
and   city_id = 1 
and   spec_id= 1 
and company_id = ifnull (NULLIF(2, 0), company_id) 
and slot_date ='2017-04-02' 
order by from_time ; 

Answer 1

要获得一行，您应该使用LIMIT 1，而不是MIN()列表中的SELECT。

select *, STR_TO_DATE(concat(slot_date, ' ' , sec_to_time(from_time)),  '%Y-%m-%d %H:%i') next_available_slot
from  appt_available_slots
where country_id = 1 
and   city_id = 1 
and   spec_id= 1 
and company_id = ifnull (NULLIF(2, 0), company_id) 
and slot_date ='2017-04-02' 
order by from_time
limit 1