如何计算 ROR 中特定字段中具有唯一值的记录数? [英] How can I count the number of records that have a unique value in a particular field in ROR?

问题描述

我有一个包含日期字段的记录集，我想确定记录集中代表了多少个唯一日期.

I have a record set that includes a date field, and want to determine how many unique dates are represented in the record set.

类似于:

Record.find(:all).date.unique.count 

当然，这似乎行不通.

推荐答案

你想要的是以下 SQL:

What you're going for is the following SQL:

SELECT COUNT(DISTINCT date) FROM records

ActiveRecord 内置了这个:

ActiveRecord has this built in:

Record.count('date', :distinct => true)

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