Mysql 使用左联接和按顺序排序时如何避免文件排序

我有3个表：accounts、contacts和accounts\u contacts映射表。 我在每个表中都有大约一百万条记录。此查询正在使用filesort，运行时间超过一分钟：

explain SELECT contacts.salutation salutation, contacts.first_name first_name, contacts.last_name last_name, contacts.title title, jt0_accounts.id account_id, jt0_accounts.name account_name

FROM contacts

LEFT JOIN accounts_contacts jt1_accounts_contacts ON (contacts.id = jt1_accounts_contacts.contact_id AND jt1_accounts_contacts.deleted = 0)

LEFT JOIN accounts jt0_accounts ON (jt0_accounts.id = jt1_accounts_contacts.account_id AND jt0_accounts.deleted = 0)

ORDER BY jt0_accounts.name DESC;

这是解释输出：

id  select_type table   type    possible_keys   key key_len ref rows    Extra
1    SIMPLE contacts    ALL NULL    NULL    NULL    NULL    195634  Using temporary; Using filesort
1    SIMPLE jt1_accounts_contacts   ref idx_contid_del_accid    idx_contid_del_accid    113 sugar7.contacts.id,const    1   
1   SIMPLE  jt0_accounts    eq_ref  PRIMARY,idx_accounts_id_del,idx_accounts_date_entered,idx_accnt_assigned_del    PRIMARY 108 sugar7.jt1_accounts_contacts.account_id 1   

如您所见，contacts表正在contacts表上使用filesort

我尝试通过在ORDER by之前添加WHERE jt0_accounts.name来摆脱filesort，使其成为：

explain SELECT contacts.salutation salutation, contacts.first_name first_name, contacts.last_name last_name, contacts.title title, jt0_accounts.id account_id, jt0_accounts.name account_name

FROM contacts

LEFT JOIN accounts_contacts jt1_accounts_contacts ON (contacts.id = jt1_accounts_contacts.contact_id AND jt1_accounts_contacts.deleted = 0)

LEFT JOIN accounts jt0_accounts ON (jt0_accounts.id = jt1_accounts_contacts.account_id AND jt0_accounts.deleted = 0)

WHERE jt0_accounts.name <> ''
ORDER BY jt0_accounts.name DESC;

idx\u account\u contact索引由account\u id和contacts\u id组成。我尝试将它们添加到WHERE子句中，但似乎没有任何区别

如有任何建议，将不胜感激。

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谢谢。

对于您的查询，您可能无能为力。但是，如果将查询更改为使用内部联接，则可能有机会：

SELECT c.salutation, c.first_name, c.last_name, c.title,
       a.id as account_id, a.name as account_name
FROM accounts a JOIN
     accounts_contacts ac
     ON a.id = ac.account_id AND a.deleted = 0
     contacts c JOIN
     ON c.id = ac.contact_id AND ac.deleted = 0     
ORDER BY a.name DESC;

---

然后，尝试以下索引：accountsname，deleted，id，accounts\u contacts account\u id，contact\u id，和concats contact\u id，deleted。

除非我弄错了，否则我认为使用内部联接对我不起作用。因为我想显示联系人表中的所有记录，即使它没有关联的帐户。内部联接的性能很好。我可以在原始查询中将LEFT替换为INNER，并很快得到结果。但结果并不是我所期望的。

SELECT c.salutation, c.first_name, c.last_name, c.title,
       a.id as account_id, a.name as account_name
FROM accounts a JOIN
     accounts_contacts ac
     ON a.id = ac.account_id AND a.deleted = 0
     contacts c JOIN
     ON c.id = ac.contact_id AND ac.deleted = 0     
ORDER BY a.name DESC;