mysql - 需要帮助提高 SQL 性能（子查询与联接）

Question

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

我需要一个不同客户的列表，其中最近的活动是在去年输入的。我已经让下面的代码工作了，但它非常慢，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

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'
)

我什至不确定您是否需要distinct此配置中的任何一个。