mysql - 当我在单个查询中使用 sum 和 count 时，我得到不正确的结果

Question

对于以下查询：

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

J如果您有 3 条记录和 4 条记录，您应该尽快将 SUM 和 COUNT 从不同的表中分离出来，ID您在结果集中 JOIN 后得到 3*4=12 条记录，因此您得到错误的总和和计数。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