SELECT DATE(del_sendmsg_records.send_date) AS oneday,del_branchs.name AS del_branch_name, del_branchs.shortname AS del_branch_shortname, COUNT(*) AS number
FROM del_sendmsg_records
JOIN del_branchs
ON del_sendmsg_records.del_branch_id=del_branchs.id
WHERE del_sendmsg_records.sended=1
GROUP BY oneday,del_sendmsg_records.del_branch_id
这个应该怎么优化啊,目测是因为这个才慢WHERE del_sendmsg_records.sended=19(sendedtinyint(1) NOT NULL是否已发送,0未发送,1发送)应该怎么优化