Use different user.construct_public_followings_sql query depending on database backend.

This is done for performance reasons as a temporary fix for problems with 0.4.0.0 on MySQL. This madness is explained in issue https://github.com/diaspora/diaspora/issues/5014.

(cherry picked from commit 80075c13f4)

app/models/user/querying.rb

@@ -69,7 +69,16 @@ module User::Querying
 
   def construct_public_followings_sql(opts)
     Rails.logger.debug("[EVIL-QUERY] user.construct_public_followings_sql")
+    
+    # For PostgreSQL and MySQL/MariaDB we use a different query
+    # see issue: https://github.com/diaspora/diaspora/issues/5014
+    if AppConfig.postgres?
       query = opts[:klass].where(:author_id => Person.in_aspects(opts[:by_members_of]).select("people.id"), :public => true, :pending => false)
+    else
+      aspects = Aspect.where(:id => opts[:by_members_of])
+      person_ids = Person.connection.select_values(people_in_aspects(aspects).select("people.id").to_sql)
+      query = opts[:klass].where(:author_id => person_ids, :public => true, :pending => false)
+    end
 
     unless(opts[:klass] == Photo)
       query = query.where(:type => opts[:type])