module Gitlab module SQL # Class for building SQL UNION statements. # # ORDER BYs are dropped from the relations as the final sort order is not # guaranteed any way. # # Example usage: # # union = Gitlab::SQL::Union.new(user.personal_projects, user.projects) # sql = union.to_sql # # Project.where("id IN (#{sql})") class Union def initialize(relations, remove_duplicates: true) @relations = relations @remove_duplicates = remove_duplicates end def to_sql # Some relations may include placeholders for prepared statements, these # aren't incremented properly when joining relations together this way. # By using "unprepared_statements" we remove the usage of placeholders # (thus fixing this problem), at a slight performance cost. fragments = ActiveRecord::Base.connection.unprepared_statement do @relations.map { |rel| rel.reorder(nil).to_sql }.reject(&:blank?) end if fragments.any? fragments.join("\n#{union_keyword}\n") else 'NULL' end end def union_keyword @remove_duplicates ? 'UNION' : 'UNION ALL' end end end end