db.getCollection("vocsdatas").aggregate([
{$match:{devname:{$regex:'North side of the park (Lvyi Substation)'}}},
{$group:{_id : "$sendtime",devname:{$max:"$devname"},qyname:{$max:"$qyname"},no:{$max:"$no"},no2:{$max:"$ no2 "},nox:{$max:"$nox"},nh3:{$max:"$nh3"},wendu:{$max:"$wendu"},shidu:{$max:"$shidu" } ,fengsu:{$max:"$fengsu"},fengxiang:{$max:"$fengxiang"},ben:{$max:"$ben"},jiaben:{$max:"$jiaben"}, yiben :{$max:"$yiben"},yiererjiaben:{$max:"$yiererjiaben"},jianduierjiaben:{$max:"$jianduierjiaben"},jiawan:{$max:"$jiawan"},feijiawanzongting: { $max:"$feijiawanzongting"},so2:{$max:"$so2"},h2s:{$max:"$h2s"}}},
{$project:{_id:0,sendtime:" $ _id",devname:1,qyname:1,no:1,no2:1,nox:1,nh3:1,wendu:1,shidu:1,fengsu:1,fengxiang:1,ben:1,jiaben: 1 ,yiben:1,yiererjiaben:1,jianduierjiaben:1,jiawan:1,feijiawanzongting:1,so2:1,h2s:1}},
{$sort:{sendtime:-1}},
{$skip :20},
{$limit:10}
]
)
