使用exists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()")

感谢您的帮助！

Answer 1

基于存在的SQL语法

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