有没有办法在Rails 3中使用MySQL UNION?
I think the only way you're going to get this to work by directly executing the query.
ActiveRecord::Base.connection.execute("SELECT REPEAT('a',1) UNION SELECT REPEAT('b',10)")
This returns an ActiveRecord resultset. If you want the results wrapped in a model do something like this:
MyModel.find_by_sql("...")
I found a neat hack using select . For example if you want to make a union between User and OtherUser .
User.select('id from other_users union select id')
this will generate this SQL
"SELECT id from other_users union select id FROM users "
Model.find_by_sql("your union query")
As you can read on this thread there are people working on a better solution for creating union queries in Rails:
https://github.com/rails/arel/pull/118
Meanwhile, I have written an small hack with which you'll be able to create simple union queries and do some filters with DISTINCT, ORDER BY and LIMIT:
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