IF you want to select unique values from a column in ActiveRecord, you can use distinct + pluck.
Model.distinct.pluck(:column)
For example:
User.distinct.pluck(:id)
# (0.1ms) SELECT DISTINCT "users"."id" FROM "users"
You can also get unique values from multiple columns.
User.distinct.pluck(:id, :name)
# (0.1ms) SELECT DISTINCT "users"."id", "users"."name" FROM "users"