Question

如何提高下面给出的查询性能

select 
     distinct o1.id as c1, 
              a1.id as c2,
              o1.t1_id as c3, 
              o1.t2_id as c4,
              o1.t_p_id as c5 
from 
     ord o1 
     left outer join 
     acc a1 
       on o1.end_user_id=a1.id 
     left outer join 
     acc a2 
       on 1.t1_id=a2.id 
     left outer join 
     acc a3 
       on o1.t2_id=a3.id 
     left outer join 
     acc a4 on 
       o1.t_p_id=account4_.id 
where 
     a1.account_id=1 or a2.account_id=1 or a3.account_id=1 or a4.account_id=1;

Answer 1

在我看来，同一个acc表上的这么多左外连接可能是造成性能问题的原因。

我建议弄清楚你的意图，然后尝试在同一张桌子上消除这么多左连接。

对于一般分析，我认为@ScottMarlowe是对的，你需要提供更多的信息，比如索引，解释结果等......

Answer 2

我不是专家，但从我的观点来看，你可以使用'exists'命令而不是'left join'。

我尝试使用'exists'命令编写您的查询，如下所示：

select 
     distinct o1.id as c1, 
              a1.id as c2,
              o1.t1_id as c3, 
              o1.t2_id as c4,
              o1.t_p_id as c5 
from ord o1 
        where exists (select 1 
                        from acc a1 where o1.end_user_id=a1.id and a1.account_id=1)
        or exists (select 1 
                        from acc a2 where o1.end_user_id=a2.id and a2.account_id=1)  
        or exists (select 1 
                        from acc a3 where o1.end_user_id=a3.id and a3.account_id=1)  
        or exists (select 1 
                        from acc a4 where o1.end_user_id=a4.id and a4.account_id=1);

我希望它有所帮助。

postgresql中的左外连接性能问题

2 个答案: