Revert "Merge pull request #8209 from senny/backport_8176"

This reverts commit 724020278480855bddfe749c91f1074d4f50f3c6, reversing
changes made to e4e2bcce75b85fb8c1c49509a17bd5dfe6034c32.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/relation/calculations.rb
	activerecord/test/cases/calculations_test.rb

Reason: This caused a regression since it changed the behavior in a
stable release.

Fixes #9777

3 files changed, 11 insertions, 6 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index c372f94729..117e527133 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,12 @@
 ## unreleased ##
 
+*   Revert changes on `pluck` that was ignoring the select clause when the relation already
+    has one. This caused a regression since it changed the behavior in a stable release.
+
+    Fixes #9777.
+
+    *Rafael Mendonça França*
+
 *   Confirm a record has not already been destroyed before decrementing counter cache.
 
     *Ben Tucker*
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index 1f9dbdc3d4..71d33fcd4e 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -183,9 +183,8 @@ module ActiveRecord
         column_name = column_name.to_s
       end
 
-      relation = clone
-      relation.select_values = [column_name]
-      klass.connection.select_all(relation.arel).map! do |attributes|
+      column_name = column_name.to_s
+      klass.connection.select_all(select(column_name).arel).map! do |attributes|
         klass.type_cast_attribute(attributes.keys.first, klass.initialize_attributes(attributes))
       end
     end
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index a1dc1de38d..b9050c750f 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -493,9 +493,8 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal [1,2,3,4], Topic.order(:id).pluck("topics.id")
   end
 
-  def test_pluck_replaces_select_clause
-    taks_relation = Topic.select([:approved, :id]).order(:id)
-    assert_equal [1,2,3,4], taks_relation.pluck(:id)
+  def test_pluck_does_not_replace_select_clause
+    taks_relation = Topic.select("approved, id, id AS foo_id").order(:foo_id)
     assert_equal [false, true, true, true], taks_relation.pluck(:approved)
   end