需要帮助提高SQL性能（子查询与连接）

Question

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

我需要一个不同客户的列表，其中最近一次活动是在去年输入的。 我已经得到了以下代码，但它很慢，因此无用。 我相信一个连接（没有子查询）会更快，但我无法弄明白。 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

尝试这个：

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

你的意思是这样的吗？

  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'";

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'
)

我甚至不确定你是否需要在这种配置中distinct 。