Add add_sequence migration helper need to fix spec

lib/gitlab/database/migration_helpers.rb

@@ -1506,6 +1506,13 @@ def drop_sequence(table_name, column_name, sequence_name)
         SQL
       end
+      def add_sequence(table_name, column_name, sequence_name, value)
+        execute <<~SQL
+          CREATE SEQUENCE #{sequence_name} START #{value};
+          ALTER TABLE #{quote_table_name(table_name)} ALTER COLUMN #{quote_column_name(column_name)} SET DEFAULT nextval('#{sequence_name}')
+        SQL
+      end
+
       private
       def create_temporary_columns_and_triggers(table, columns, primary_key: :id, data_type: :bigint)

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -3289,4 +3289,12 @@ def setup
       model.drop_sequence(:test_table, :test_column, :test_table_id_seq)
     end
   end
+
+  describe '#add_sequence' do
+    it "executes the statement to add the sequence" do
+      expect(model).to receive(:execute).with /CREATE SEQUENCE test_table_id_seq START 1;\nALTER TABLE "test_table" ALTER COLUMN "test_column" SET DEFAULT nextval('test_table_id_seq')/
+
+      model.add_sequence(:test_table, :test_column, :test_table_id_seq, 1)
+    end
+  end
 end