如何在rails的两个列上实现唯一的索引

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:

我有一个表，我想在两列上添加一个唯一的索引。这些列也被索引。所以我的问题是，如果我只删除一个列的索引，或者我必须使用这三个索引:

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

Thanks for your clarification Markus

谢谢你的澄清，马库斯

1 个解决方案

#1

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