需要幫助提高SQL性能（子查詢與聯接）

Question

我有2個表（AllClients & AllActivities），並需要檢索以下信息：

我需要在那裏最近的活動已被輸入不同的客戶名單去年。我已經得到了下面的代碼來工作，但它很痛苦地慢，因此沒有用。我相信一個連接（沒有子查詢）會更快，但我無法弄清楚。這是我當前的SQL語句：

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

試試這個：

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

你的意思是這樣？

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' 
) 

我甚至不確定在這個配置中需要distinct。