Calculating the average days between records in Rails

Given that I have a Foo model w/ the standard Rails timestamp columns what would be the most efficient way to calculate the average number of days between records being created?

Answers


The maximum and minimum class methods of your model will use the SQL aggregate functions min() and max() to find the extreme values efficiently.

span_secs = Foo.maximum(:created_at) - Foo.minimum(:created_at)
avg_secs = span_secs / (Foo.count - 1)
avg_days = avg_secs / (24 * 60 * 60)

If you use MySQL

secs = Foo.where("created_at IS NOT NULL").average("UNIX_TIMESTAMP(created_at)").to_i
DateTime.strptime secs.to_s, "%s"

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