这不需要子查询，因为mysql允许在 group by （并非所有数据库都这样做）。所以：

Select customer_id,
       (case when call_details = 'International'
             then 'International Calls'
             else 'National Calls'
        end) as call_group,
       sum(minutes) 
from call_minutes 
where date between '$from' and '$to' 
group by customer_id, call_group;

注意：这假设您希望每个客户都有单独的行。如果没有，请移除 customer_id 从两个 select 以及 group by :

Select (case when call_details = 'International'
             then 'International Calls'
             else 'National Calls'
        end) as call_group,
       sum(minutes) 
from call_minutes 
where date between '$from' and '$to' 
group by call_group;

如果您想要每个组中的客户id列表，您可以随时添加 group_concat(customer_id) .

使用以下sql：

select customer_id,
       call_details,
       sum(minutes) as minutes
from(
Select customer_id,
       if (call_details ='International' , 'International Calls', 'National Calls') as call_details,
       minutes
from call_minutes 
where date between '$from' and '$to') x 
group by customer_id,call_details