我有一个包含日期字段的记录集，要确定有多少独特的日期psented的记录集重$ P $。

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

是这样的：

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

但当然，这似乎并没有工作。

but of course, that doesn't seem to work.

推荐答案

什么你要去的是SQL语句：

What you're going for is the following SQL:

SELECT COUNT(DISTINCT date) FROM records

ActiveRecord的是这个内置的：

ActiveRecord has this built in:

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