问题描述
我在Active Record文档中看到，您可以使用大于/小于比较来查询日期。但是，如果要选择date = Date.today，或者我必须查询大于昨天而小于明天的日期该怎么办？
I see in the Active Record docs, you can query for a date using a greater than / less than comparison. However, what if you want to select where date = Date.today or must I query where date is greater than yesterday and less than tomorrow?
正如您所看到的，我在以下查询中确实这样做，并且查询Date =今天返回空集的地方
As you can see, I'm doing exactly that in the following queries and querying where Date = today returns an empty set
1.9.3p286 :096 > Subscription.where("created_at = ?", Date.today).count
(0.5ms) SELECT COUNT(*) FROM `subscriptions` WHERE (created_at = '2013-01-18')
=> 0
vs。
1.9.3p286 :098 > Subscription.where("expiration_date < ? AND expiration_date > ?", Date.today + 1, Date.today - 1).count
(0.4ms) SELECT COUNT(*) FROM `subscriptions` WHERE (expiration_date < '2013-01-19' AND expiration_date > '2013-01-17')
=> 1
这是查询今天日期的正确方法还是我遗漏了什么？
Is this the proper way to query for today's date or am I missing something?
推荐答案
我认为这是此问题的DUP：
I think this is a DUP of this question:
Subscription.where("DATE(created_at) = ?", Date.today).count
我很确定这可以在MySQL和PostgreSQL中使用，但是我不确定这是否是SQL标准。
I'm pretty sure this works in MySQL and PostgreSQL, but I'm not sure if it's a SQL standard.
维基百科似乎认为 TO_DATE 将是标准：
Wikipedia seems to think TO_DATE would be the standard:http://en.wikipedia.org/wiki/SQL#Date_and_time
这在PostgreSQL中对我不起作用。
That didn't work for me in PostgreSQL though.
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