当我在单个查询中使用sum和count时，我得到的结果不正确

Question

用于以下查询：

select sum(j.credits) as credits, count(id.redo) as redos 
from operator o inner join jobdetails j on j.opid=o.id 
                inner join imagedetails id on id.opid=o.id 
                and im.redo=y group by o.id 

Answer 1

如果在J中有3条记录，并且ID中的4条记录在结果集中的JOIN之后得到3 * 4 = 12条记录，则应立即将SUM和COUNT从不同的表中分开，这样您就可以了得到错误的总和和数。例如：

select o.id, j.sum_credits as credits, id.count_redo as redos 
from operator o 
    inner join 
       (select opid, sum(credits) sum_credits from jobdetails group by opid) j 
               on j.opid=o.id 
    inner join 
        (select opid, count(redo) count_redo from imagedetails 
                                              where redo=y group by opid) id 
               on id.opid=o.id