1
我正在将SQL查询迁移到Active Record。这里是一个简化版本:如何获得Active Record中的子查询计数?
SELECT count(*) FROM (
SELECT type, date(created_at)
FROM notification_messages
GROUP BY type, date(created_at)
) x
我不知道如何在Active Record中实现这个。这工作,但它是凌乱:
sql = NotificationMessage.
select("type, date(created_at) AS period").
group("type", "period").
to_sql
NotificationMessage.connection.exec_query("SELECT count(*) FROM (#{sql}) x")
另一种可能性是做在Ruby中计数,但是这将是效率较低:
NotificationMessage.
select("type, date(created_at) AS period").
group("type", "period").
length
有没有更好的解决办法?