1.查詢每個(gè)用戶最新的發(fā)言記錄：

select max(time) from 2017sxgf group by id order by time desc limit 10;

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2.找到發(fā)言數(shù)最多的用戶ID和次數(shù)

select userid,count(userid) from orders ?where userid != ” group by userid order by count(userid) desc ?limit 1;

3.關(guān)于MySQL中每個(gè)用戶取1條記錄的三種寫法

第一種是先排序，然后group，這樣的話自然可以取到最適合的一條數(shù)據(jù)。
缺點(diǎn)很明顯：Using temporary; Using filesort

select * from (select * from 2017sxgf order by time desc)t group by mobile limit 10;

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第二種是聯(lián)合查詢?

select * from (select max(time) as btime ?from 2017sxgf group by mobile limit 10)t left join ?2017sxgf as s on t.btime = s.time;

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第三種是子查詢

select * from 2017sxgf where exists(select mobile from (select max(time) as btime from 2017sxgf ?group by mobile limit 10)t where t.btime = 2017sxgf.time);

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5.

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