如何在Postgres的Rails中按天分组和计数？ [英] How to group and count by day in Rails in Postgres?

问题描述

这样的问题如何按天分组而不是按日分组日期？显示了如何在Ruby中进行分组。

This SO question How do I group by day instead of date? shows how to group in Ruby.

此方法有效，但对于大量记录而言将非常慢。
如何做到在Postgres中按天进行：created_at 的分组和计数？

This works, but is going to be very slow for a large number of records. How to do it so that the grouping and counting by :created_at by day happens within Postgres?

推荐答案

如果尚未定义订单范围，则可以使用postgres中的 date（）方法，如下所示：

If you haven't an order scope defined, you can use date() method from postgres, like this:

Post.select("date(created_at) as created_date").group("created_date")

如果您有订单范围：

Post.all.except(:order).
     select("date(created_at) as created_date").group("created_date")

您必须定义选择字段才能进行自定义分组，因此 select（）部分应包含您需要记录集包含的字段。

You will have to define select fields in order to have a custom grouping, so the select() part should contain the fields you need your recordset to contain.

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