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select count(d.num),d.num,e.mvid,e.enterDate,e.dayOrNight,e.deviceNum
from enter e,deviceNum d
where e.deviceNum=d.id
and e.mvid='b4df840927e6483db7a13a5e8d5b6166'
and e.enterDate='2018-03-08'
and e.dayOrNight='白班'
group by e.mvid,e.enterDate,e.dayOrNight ,e.deviceNum,d.id,d.num
order by d.num
为什么总共16条记录，count却是18 ？
from enter e,deviceNum d
where e.deviceNum=d.id
and e.mvid='b4df840927e6483db7a13a5e8d5b6166'
and e.enterDate='2018-03-08'
and e.dayOrNight='白班'
group by e.mvid,e.enterDate,e.dayOrNight ,e.deviceNum,d.id,d.num
order by d.num
为什么总共16条记录，count却是18 ？
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浅笑天无情 2018-03-09
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group by 的原因，count()是总条数，有2条数据被汇总了
