instance method `subquery_for`

Ruby on Rails 4.2.9

Since v4.0.13 Last seen in v5.2.8.1

Available in: v4.0.13 v4.1.16 v4.2.9 v5.2.8.1

Compare with:

subquery_for(key, select)

MySQL is too stupid to create a temporary table for use subquery, so we have to give it some prompting in the form of a subsubquery. Ugh!

Parameters

key req
select req

Source

# File activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb, line 735
      def subquery_for(key, select)
        subsubselect = select.clone
        subsubselect.projections = [key]

        # Materialize subquery by adding distinct
        # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
        subsubselect.distinct unless select.limit || select.offset || select.orders.any?

        subselect = Arel::SelectManager.new(select.engine)
        subselect.project Arel.sql(key.name)
        subselect.from subsubselect.as('__active_record_temp')
      end

Defined in activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb line 735 · View on GitHub · Improve this page · Find usages on GitHub

Defined in ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter

Signature

Parameters