pluck vs. select

pluck

In Rails, we have pluck, which returns an array with the values of the attributes you selected.

Doctor.pluck(:id)
   (0.9ms)  SELECT "doctors"."id" FROM "doctors"
=> [1, 3, 7, 8, 9, 5]

If you pass more than one attribute, the pluck returns an array of multiple attributes.

Doctor.pluck(:id, :updated_at)
   (0.5ms)  SELECT "doctors"."id", "doctors"."updated_at" FROM "doctors"
=> [[1, Wed, 23 Jan 2019 11:44:27.924159000 EST -05:00],
 [3, Tue, 29 Jan 2019 15:47:30.056920000 EST -05:00],
 [7, Thu, 28 May 2020 19:30:29.238601000 EDT -04:00],
 [8, Thu, 28 May 2020 19:30:29.251257000 EDT -04:00],
 [9, Sat, 26 Jun 2021 19:56:41.536687000 EDT -04:00],
 [5, Tue, 28 Jun 2022 16:49:45.091360000 EDT -04:00]]

The query is precise to get only the attributes you are asking for.

SELECT "doctors"."id", "doctors"."updated_at" FROM "doctors"

select

The select make the same query.

Doctor.select(:id, :updated_at)
  Doctor Load (0.3ms)  SELECT "doctors"."id", "doctors"."updated_at" FROM "doctors"

Doctor.pluck(:id, :updated_at)
   (0.3ms)  SELECT "doctors"."id", "doctors"."updated_at" FROM "doctors"

Doctor.select(:id, :updated_at)
  Doctor Load (0.6ms)  SELECT "doctors"."id", "doctors"."updated_at" FROM "doctors"
=>[#<Doctor:0x0000000111a2ec40 id: 1, updated_at: Wed, 23 Jan 2019 11:44:27.924159000 EST -05:00>,
 #<Doctor:0x0000000111a2eab0 id: 3, updated_at: Tue, 29 Jan 2019 15:47:30.056920000 EST -05:00>,
 #<Doctor:0x0000000111a2e998 id: 7, updated_at: Thu, 28 May 2020 19:30:29.238601000 EDT -04:00>,
 #<Doctor:0x0000000111a2e858 id: 8, updated_at: Thu, 28 May 2020 19:30:29.251257000 EDT -04:00>,
 #<Doctor:0x0000000111a2e4c0 id: 9, updated_at: Sat, 26 Jun 2021 19:56:41.536687000 EDT -04:00>,
 #<Doctor:0x0000000111a2e218 id: 5, updated_at: Tue, 28 Jun 2022 16:49:45.091360000 EDT -04:00>]

But select returns an ActiveRecord_Relation with objects from the model where it was called.

Doctor.select(:id, :updated_at).class
=> Doctor::ActiveRecord_Relation

that's all folks :)