mysql - 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，其中最近的事件已在去年输入。我已经使用了以下代码，但速度非常慢，因此没有用。我相信加入(没有子查询)会更快，但我就是想不通。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';