需要幫助提高SQL性能（子查詢與連接）

Question

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

我需要一個不同客戶的列表，其中最近一次活動是在去年輸入的。 我已經得到了以下代碼，但它很慢，因此無用。 我相信一個連接（沒有子查詢）會更快，但我無法弄明白。 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

嘗試這個：

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

你的意思是這樣的嗎？

  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'
)

我甚至不確定你是否需要在這種配置中distinct 。