MySQL 求和列并将其与给定值进行比较

Question

我需要显示一组来自数据库的可用空间结果，条件是:

1. alm_num = 1
2. alm_date 2012 年 11 月 26-29 日
3. 和 sum_num > or = 3

然后我这样编写 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'

但是我有:

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

那么你们能否建议我如何从这个错误中幸存下来。 问候，

Answer 1

您需要对聚合列的条件使用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添加一个group by 子句，这是我为您添加的。