Math with datetime in SQL query in rails

问题

So I have an table of phone_numbers in Rails 3.2, and I would like to be able to make a query such as the following:

PhoneNumber.where("last_called_at - #{Time.now} > call_spacing * 60")

where last_called_at is a datetime and call_spacing is an integer, representing the number of minutes between calls.

I have tried the above, I have also tried using

PhoneNumber.where("datediff(mi, last_called_at, #{Time.now}) > call_spacing")

If anyone could help me make this work, or even recommend a current, up-to-date rails SQL gem, I would be very grateful.

Edit: So the best way to make this work for me was to instead add a ready_at column to my database, and update that whenever either call_spacing or last_called_at was updated, using the before_save method. This is probably the most semantic way to approach this problem in rails.

回答1:

You have to use quotes around #{Time.now}. To make your first query work you may use TIME_TO_SEC() function:

PhoneNumber.where("(TIME_TO_SEC('#{Time.now}') - TIME_TO_SEC(last_called_at)) > (call_spacing * 60)")

Here is my way to do this:

PhoneNumber.where("last_called_at > '#{Time.zone.now.utc - (call_spacing * 60)}'")

also take a look at this article to be aware of how to play with timezones:

http://danilenko.org/2012/7/6/rails_timezones/

来源：https://stackoverflow.com/questions/17514539/math-with-datetime-in-sql-query-in-rails