Add Gitlab::Database::Subquery.self_join to delete_all with limit

`delete_all` doesn't support limit, so you'd need to subquery
that. And instead of subquerying with `where(id: query)`, it's better
to use an `INNER JOIN`. This method also works with MySQL, while
subquerying doesn't (without another layer of subquerying)

Reference:
https://stackoverflow.com/questions/17892762/mysql-this-version-of-mysql-doesnt-yet-support-limit-in-all-any-some-subqu/17892886#17892886

1 files changed, 17 insertions, 0 deletions

diff --git a/spec/lib/gitlab/database/subquery_spec.rb b/spec/lib/gitlab/database/subquery_spec.rb
new file mode 100644
index 00000000000..70380e02f16
--- /dev/null
+++ b/spec/lib/gitlab/database/subquery_spec.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Database::Subquery do
+  describe '.self_join' do
+    set(:project) { create(:project) }
+
+    it 'allows you to delete_all rows with WHERE and LIMIT' do
+      events = create_list(:event, 8, project: project)
+
+      expect do
+        described_class.self_join(Event.where('id < ?', events[5]).recent.limit(2)).delete_all
+      end.to change { Event.count }.by(-2)
+    end
+  end
+end