如何在rails中的两列上实现唯一索引 [英] How to implement a unique index on two columns in rails

问题描述

我有一张表，我正在尝试在两列上添加唯一索引.这些列也被索引.所以我的问题是我是否可以删除仅用于一列的索引，或者我是否必须使用所有三个索引:

I have a table and I'm trying to add a unique index on two columns. Those columns are also indexed. So my question is if I just can remove the indexes who were just for one column or if I have to use all three indexes:

add_index "subscriptions", ["user_id"]
add_index "subscriptions", ["content_id"]
add_index "subscriptions", ["user_id"], ["content_id"], :unique => true

推荐答案

add_index :subscriptions, [:user_id, :content_id], unique: true

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