mysql update left join

先验证

select u.md5,u.id as uid,a.id as aid,u.dlcount
from zb_url u 
left join  zb_article partition(p0, p2017) a on u.md5=a.url_md5
where u.dlcount > 0 and a.id is null

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再执行

update zb_url a
left join zb_article partition(p0, p2017) b
on a.md5=b.url_md5
set a.dlcount=0
where a.dlcount>0 and b.id is null

参考资料

https://stackoverflow.com/a/806925/2007704