需要帮助提高SQL性能（子查询与联接）

Question

我有2个表（AllClients & AllActivities），并需要检索以下信息：

我需要在那里最近的活动已被输入不同的客户名单去年。我已经得到了下面的代码来工作，但它很痛苦地慢，因此没有用。我相信一个连接（没有子查询）会更快，但我无法弄清楚。这是我当前的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'"; 

Answer 1

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'; 

Answer 2

你的意思是这样？

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'"; 

Answer 3

你不需要做聚合。

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' 
) 

我甚至不确定在这个配置中需要distinct。