在 Rails 中查找数据库字段之间操作的平均值/最小值/最大值

Question

Relatively new to SQL and ORM.

Let's say I have a database table with start_at and finish_at fields (both datetime). Table contains 10000 items for example.

How to calculate the average, max/min duration (finish_at - start_at) using ruby or Active Record tools? There is no need to write it somewhere, just need numbers.

Answer 1

table = MyClass.arel_table
duration = table[:finish_at] - table[:start_at]
MyClass.pick(duration.maximum, duration.minimum, duration.average)
#=> ["125 days 20:46:34.05816", "00:00:00.063579", "20 days 23:30:16.221092"]

Cast them to another data type as needed or use directly in other queries.