MySQL sum列并将其与给定值进行比较

Question

我需要显示DB中可用房间的一组结果，条件是：

1. alm_num = 1
2. alm_date 2012年11月26日至29日之间
3. 和sum_num＆gt;或= 3

然后我像这样编写mySQL：

select sum(villas_allotment.alm_num) as sum_num, 
villas_allotment.alm_id as aid, villas_db.v_name as vname  
from villas_allotment 
inner join villas_db on villas_allotment.alm_vid=villas_db.v_id 
where alm_num='1' 
and alm_date between '2012-11-26' and '2012-11-29' 
and alm_vid='3' 
and sum_num>='3'

但我有：

#1054 - Unknown column 'sum_num' in 'where clause'

那么你们可以建议我如何从这个错误中生存下来。 的问候，

Answer 1

您需要在汇总列的条件中使用HAVING：

select
    sum(villas_allotment.alm_num) as sum_num, 
    villas_allotment.alm_id as aid,
    villas_db.v_name as vname  
from villas_allotment 
inner join villas_db on villas_allotment.alm_vid = villas_db.v_id 
where alm_num = '1' 
and alm_date between '2012-11-26' and '2012-11-29' 
and alm_vid = '3' 
group by villas_allotment.alm_id, villas_db.v_name
having sum(villas_allotment.alm_num) >= 3

您还需要在非聚合列上使用group by子句，我已为您添加了这些子句。