请问一下,select count(date1)/count(date0) as avg_ret from ( select distinct date(t.date) as date0, t.device_id, t1.date as date1 from question_practice_detail as t left join question_practice_detail as t1 on t1.device_id=t.device_id and datediff(date(t1.date),date(t.date))=1 order by date0 ) as a 这样的作法提交也是正确的,但是否只是巧合有漏洞?
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05-09 13:22
门头沟学院 Java
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