Mongodb 聚合Aggregation中$sum:1 后面的1是什么意思

源数据:

{"_id" : "GuqXmAkkARqhBDqhy","beatmapset_id" : "342537","version" : "MX","diff_approach" : "5","artist" : "Yousei Teikoku","title" : "Kokou no Sousei","difficultyrating" : "3.5552737712860107"
}
{"_id" : "oHLT7KqsB7bztBGvu","beatmapset_id" : "342537","version" : "HD","diff_approach" : "5","artist" : "Yousei Teikoku","title" : "Kokou no Sousei","difficultyrating" : "2.7515676021575928"
}
{"_id" : "GbotZfrPEwW69FkGD","beatmapset_id" : "342537","version" : "NM","diff_approach" : "5","artist" : "Yousei Teikoku","title" : "Kokou no Sousei","difficultyrating" : "0"
}

 然后运行以下的命令:
 

db.getCollection('dup_case').aggregate(
[
{$group:{_id:{diff_approach:'$diff_approach'},count:{$sum:2}}},
{$match:{count:{$gt:1}}}
]
)

 
 
返回的count是6
 
所以
$sum:1 的含义:
如果前面的情况出现一次,就加1, 如果后面$sum:2 那么每次前面条件满足一次就加2

本文来自互联网用户投稿，文章观点仅代表作者本人，不代表本站立场，不承担相关法律责任。如若转载，请注明出处。 如若内容造成侵权/违法违规/事实不符，请点击【内容举报】进行投诉反馈！