3 files changed, 12 insertions, 5 deletions
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index 648fdd0dc4..98f57549a5 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -112,7 +112,7 @@ db_namespace = namespace :db do
       end
     end
 
-    # desc  'Rollbacks the database one migration and re migrate up (options: STEP=x, VERSION=x).'
+    desc "Rolls back the database one migration and re-migrates up (options: STEP=x, VERSION=x)."
     task redo: :load_config do
       raise "Empty VERSION provided" if ENV["VERSION"] && ENV["VERSION"].empty?
 
@@ -128,7 +128,7 @@ db_namespace = namespace :db do
     # desc 'Resets your database using your migrations for the current environment'
     task reset: ["db:drop", "db:create", "db:migrate"]
 
-    # desc 'Runs the "up" for a given migration VERSION.'
+    desc 'Runs the "up" for a given migration VERSION.'
     task up: :load_config do
       ActiveRecord::Tasks::DatabaseTasks.raise_for_multi_db(command: "db:migrate:up")
 
@@ -162,7 +162,7 @@ db_namespace = namespace :db do
       end
     end
 
-    # desc 'Runs the "down" for a given migration VERSION.'
+    desc 'Runs the "down" for a given migration VERSION.'
     task down: :load_config do
       ActiveRecord::Tasks::DatabaseTasks.raise_for_multi_db(command: "db:migrate:down")
 
@@ -230,7 +230,7 @@ db_namespace = namespace :db do
     db_namespace["_dump"].invoke
   end
 
-  # desc 'Drops and recreates the database from db/schema.rb for the current environment and loads the seeds.'
+  desc "Drops and recreates the database from db/schema.rb for the current environment and loads the seeds."
   task reset: [ "db:drop", "db:setup" ]
 
   # desc "Retrieves the charset for the current environment's database"
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 87a53966e4..6a181882ae 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -952,7 +952,7 @@ module ActiveRecord
     def optimizer_hints!(*args) # :nodoc:
       args.flatten!
 
-      self.optimizer_hints_values += args
+      self.optimizer_hints_values |= args
       self
     end
 
diff --git a/activerecord/test/cases/relation_test.rb b/activerecord/test/cases/relation_test.rb
index e0743de94b..e74fb1a098 100644
--- a/activerecord/test/cases/relation_test.rb
+++ b/activerecord/test/cases/relation_test.rb
@@ -363,6 +363,13 @@ module ActiveRecord
       assert_match %r{/\*\+ BADHINT \*/}, post_with_hint.to_sql
     end
 
+    def test_does_not_duplicate_optimizer_hints_on_merge
+      escaped_table = Post.connection.quote_table_name("posts")
+      expected = "SELECT /*+ OMGHINT */ #{escaped_table}.* FROM #{escaped_table}"
+      query = Post.optimizer_hints("OMGHINT").merge(Post.optimizer_hints("OMGHINT")).to_sql
+      assert_equal expected, query
+    end
+
     class EnsureRoundTripTypeCasting < ActiveRecord::Type::Value
       def type
         :string