ruby-on-rails - 使用存在优化查询

Question

如何使用 EXISTS 而不是 IN 函数优化以下 mysql 查询？

Subscriber.first(:conditions => ["email IN(SELECT email from submissions WHERE url = ? AND confirmed != 0)", url], :order => "RANDOM()")

感谢帮助！

Answer 1

基于 sql 语法 for exists

EXISTS (SELECT email from submissions x WHERE url = ? AND confirmed != 0 AND x.email = email)