Question

我有来自多个表的多个嵌套选择的查询，如下所示：

select c.name,c.created_date,
(  select count(id) from user u 
   where u.company_id=c.id ) as users,
(  select count(distinct uls.user_id) from user_login_status uls 
   where uls.company_id=c.id 
     and uls.date between '2013-11-18' and '2014-01-10' ) as unique_logins,
(  select count(id) from cash_receiving cr 
   where cr.company_id=c.id 
   and cr.created_date between '2013-11-18' and '2014-01-10' ) as recognitions,
0 as licences,
(  select count(id) from inventory_item i 
   where i.company_gid=c.id ) as store_items,
(  select count(id) from award a 
   where a.company_gid=c.id ) as awards,
(  select uls2.date from user_login_status uls2 
   where uls2.company_id=c.id 
   ORDER BY uls2.date DESC LIMIT 1 ) as last_login,
 c.id as id,
 c.is_live as live 
 from company c 
 order by c.name

user_login_status包含每个用户登录的条目，因此它将包含大量数据，即sql端，就像我在上面使用实体管理器调用查询的java端一样所以我想知道上面的查询的性能，它是否适用于每个表的海量数据，或者最好做出单独的选择语句，请告知如何使上述查询表现良好，谢谢。

Answer 1

试试这个：

SELECT c.name,c.created_date, u.users, uls.unique_logins, cr.recognitions, 
       0 AS licences, i.store_items, s.awards, uls2.last_login, 
       c.id AS id, c.is_live AS live 
FROM company c 
LEFT JOIN (SELECT u.company_id, COUNT(u.id) users 
           FROM user u 
           GROUP BY u.company_id
         ) AS u ON u.company_id = c.id
LEFT JOIN (SELECT uls.company_id, COUNT(DISTINCT uls.user_id) unique_logins 
           FROM user_login_status uls WHERE uls.date BETWEEN '2013-11-18' AND '2014-01-10' 
           GROUP BY uls.company_id
         ) AS uls ON uls.company_id=c.id 
LEFT JOIN (SELECT cr.company_id, COUNT(cr.id) recognitions FROM cash_receiving cr 
           WHERE cr.created_date BETWEEN '2013-11-18' AND '2014-01-10'
           GROUP BY cr.company_id
         ) AS cr ON cr.company_id = c.id 
LEFT JOIN (SELECT i.company_gid, COUNT(i.id) store_items 
           FROM inventory_item i 
           GROUP BY i.company_gid
         ) AS  i ON i.company_gid = c.id
LEFT JOIN (SELECT a.company_gid, COUNT(a.id) awards 
           FROM award a 
           GROUP BY a.company_gid
         ) AS  a ON a.company_gid = c.id
LEFT JOIN (SELECT uls2.company_id, MAX(uls2.date) last_login 
           FROM user_login_status uls2 
           GROUP BY uls2.company_id
         ) AS uls2 ON uls2.company_id=c.id 
ORDER BY c.name

从多个表中嵌套选择的性能

1 个答案: