我有下面的查询,它从多个表中提取数据以创建更新:
UPDATE en_inter.subscribers_data AS sd
inner join en_inter.list_subscribers AS ls on sd.subscriberid = ls.subscriberid
LEFT JOIN (
SELECT pd1.email_address,COUNT(pd1.email_address) AS NumDowns
FROM email.papr_down pd1
INNER JOIN email.papr_data pd2 on pd1.paper_id = pd2.id
INNER JOIN email.papr_subj ps on ps.id = pd2.subject
INNER JOIN email.papr_exam pe on pe.id = pd2.exam
INNER JOIN email.papr_levl pl on pl.id = pd2.level
WHERE pd2.exam = 1
and pd2.level = 4
GROUP BY email_address
) AS downs ON downs.email_address = ls.emailaddress
SET sd.data = ifnull(downs.NumDowns,1)
WHERE sd.fieldid = 33;
它工作正常,但是当 papr_down 中有大量记录时,处理需要很长时间。关于如何优化它的任何想法?