Mysql 需要帮助提高SQL性能（子查询与联接）

我有两个表AllClient&AllActivities，需要检索以下信息：

我需要一个不同客户的名单，其中最近的活动已进入去年。我已经使用了下面的代码，但是速度非常慢，因此没有用处。我相信没有子查询的连接会更快，但我就是想不出来。以下是我当前的sql语句：

select  distinct(AllClients.LookupCode) 
from    AllClients 
join    (select LookupCode, 
                max(AllActivities.EnteredDate) as EnteredDate 
        from AllActivities 
        group by LookupCode) AllActivities 
on      AllClients.LookupCode = AllActivities.LookupCode 
where   AllClients.Name = '$userName' 
and     AllClients.TypeCode = 'P' and AllActivities.EnteredDate < '$oneYearAgo'";

试试这个：

select AllClients.LookupCode
from AllClients
join AllActivities on AllClients.LookupCode = AllActivities.LookupCode
where AllClients.Name = '$userName' and AllClients.TypeCode = 'P' 
group by AllClients.LookupCode
having max(AllActivities.EnteredDate) < '$oneYearAgo';

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你是说像这样的事吗

  SELECT AllClients.LookupCode
    FROM AllClients
    JOIN AllActivities
      ON AllClients.LookupCode = AllActivities.LookupCode
   WHERE AllClients.Name = '$userName'
     AND AllClients.TypeCode = 'P'
GROUP BY AllClients.LookupCode
  HAVING MAX(AllActivities.EnteredDate) < '$oneYearAgo'";

---

您不需要进行聚合

select  distinct(AllClients.LookupCode) 
from    AllClients 
where   
        AllClients.Name = '$userName' 
and     AllClients.TypeCode = 'P' 
and     exists (
    select 1 from AllActivities where AllClients.LookupCode = AllActivities.LookupCode and AllActivities.EnteredDate > '$oneYearAgo'
)

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我甚至不确定在此配置中是否需要distinct。

子查询似乎很好。您可以先将EnteredDate上的条件添加到其中，而不是在主查询外部执行。@ClaudioSantos您这样说是为了格式化吗？然后投票表决；否问题是关于查询性能而不是查询格式…：很公平，那么为什么是最好的问题呢