我要创建每小时每个小时创建的项目数量阵列, 每天 。
我追踪人们的感受,所以我的模型叫做 TrackMood 它有一个叫做mood 的栏目和时间戳。
如果有的话
TrackMood.where(mood: "good").group("hour(created_at)").count
I get something like {11=>4, 12=>2, 13=>2, 15=>1}
我这里有两个问题
1 如何把一天加到今天,这样它就不会仅仅把昨天11时创造的项目加到今天11时添加的项目上?
2 当一无所有时,我如何确保它上写到 0 ?
1) 而不是仅仅按日期的小时部分分组,而需要将相关日期的部分分组,即按小时截止的日期分组,而不列出任何比该日期更具体的具体内容。
TrackMood.where(mood: "good").group("date_format(created_at, %Y%m%d %H )").count
2) 您总是会从此电话中拿回一个散列, 即使它找不到任何组。 如果您想要检查有多少组, 您可以在其中调用 < code>. size 或 < code>. count 。
对于 PostgreSQL, 您可以使用 < a href=" http://www. plasgresql.org/docs/8.1/static/ offices- datetime.html#FUNCTOPES- DateTIME-EXTRACT" rel=" nofollow noreferrer" >date_ part
SO- post - < a href=" https://stackoverflow.com/ questions/151820511/rails-posgresql-how-to- group-queries- by- hour" >Rails & amp; Postgresql: 如何按小时分组查询?
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