问题描述
我有一个用户两个 / 日期时间列用户表： created_at 和生日。我想找到用户的出生日期是创建日期不到13年。
I have two datetime columns in a User/users table: created_at and birthdate. I'd like to find users whose birthdate is less than 13 years before their creation date.
等效Rails的如果声明将是（（created_at - 出生日期）＆LT; 13.years）
The equivalent Rails if statement would be ((created_at - birthdate) < 13.years)
我如何转换成一个ActiveRecord的查询（一个会工作在PostgreSQL的）？这甚至可能，否则我将不得不手动遍历所有记录？
How do I translate this to an ActiveRecord query (one that'll work on PostgreSQL)? Is this even possible, or will I have to iterate over all records manually?
推荐答案
要做到这一点最简单的方法是使用interval,那么它是pretty的多的Rails的版本直接音译：
The easiest way to do this is to use an interval, then it is pretty much a straight transliteration of the Rails version:
User.where(%q{created_at - birthdate < interval '13 years'})
两个时间戳（或时间戳和日期）之间的差异是一个区间，所以你只需要在右边你比较合适的值。
The difference between two timestamps (or a timestamp and a date) is an interval so you just need the appropriate value on the right side of your comparison.
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