寻求帮助－－优化SQL

[patrick1683]

select /* 70674:200 */
m.id,
substr(m.flags, 2, 1) deleted_flag,
substr(m.flags, 1, 1) read_flag,
p.id mail_to_userid,
m.subject subject,
substr(m.flags, 1, 1) read,
m.received_on received_on,
m.message_body message_desc,
substr(m.flags, 2, 1) deleted
from fgt_mail_header m
inner join cmt_person p on m.mail_to = p.id
inner join fgt_ext_notify_event e on m.event_id = e.id
inner join fgt_memo_mail_body b on m.id = b.owner_id
where m.id = m.id
and p.locale_id = e.locale_id
and m.mail_to = lower(:1)
and substr(m.flags, 2, 1) = :2
ORDER BY 6, 7 desc

cmt＿person有50万条记录，fgt_mail_header有16万条记录，执行时间为620毫秒； 希望能有优化的方法，请大俠指点优化方法。

[bfc99]

提供一下执行计划。

[mayanzs]

关键是索引，检查一下所需关联的关键字段上索引是否齐全，另fgt_mail_header表上建立substr(m.flags, 2, 1)的索引试试