Ruby-on-Rails: Selecting distinct values from the model

The docs: http://guides.rubyonrails.org/active_record_querying.html#selecting-specific-fields

Clearly state that:

query = Client.select(:name).distinct
# => Returns unique names

However, when I try that in my controller, I get the following error:

undefined method `distinct' for #<ActiveRecord::Relation:0xb2f6f2cc>

To be clear, I want the distinct names, like ['George', 'Brandon'], not the clients actual records. Is there something that I am missing?

The .distinct option was added for rails 4 which is what the latest guides refer to.

Rails 2

If you are still on rails 2 you will need to use:

Client.select('distinct(name)')

If you are on Rails 3 you will need to use:

Client.select(:name).uniq

If you look at the equivalent section of the rails 3 guide you can see the difference between the two versions.

This will work for Rails 2 (pretty old rails I know!), 3 and 4.

Client.select('distinct(name)')

This will actually use the SQL select distinct statement

SELECT distinct name FROM clients

There are some approaches:

Rails way:
```
Model.select(:name).distinct
```
Semi-rails way
```
Model.select("DISTINCT ON(models.name) models.*")
```
The second allows you to select the first record uniqued by name, but in the whole matter, not only names.

If you do not want ActiveRecord::Relations returned, just an array of the names as strings, then use:

Client.distinct.pluck(:name)

To get an ordered result set:

Client.order(:name).distinct.pluck(:name)

来源：https://stackoverflow.com/questions/18004239/ruby-on-rails-selecting-distinct-values-from-the-model

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