How can I count the number of records that have a unique value in a particular field in ROR?

Question

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

Something like:

Record         


        

Answer 1

As I mentioned here, in Rails 4, using (...).uniq.count(:user_id) as mentioned in other answers (for this question and elsewhere on SO) will actually lead to an extra DISTINCT being in the query:

SELECT DISTINCT COUNT(DISTINCT user_id) FROM ...

What we actually have to do is use a SQL string ourselves:

(...).count("DISTINCT user_id")

Which gives us:

SELECT COUNT(DISTINCT user_id) FROM ...