rails--rails/activerecord/lib/arel/visitors/mysql.rb

# frozen_string_literal: true

module Arel # :nodoc: all
  module Visitors
    class MySQL < Arel::Visitors::ToSql
      private
        def visit_Arel_Nodes_Union(o, collector, suppress_parens = false)
          unless suppress_parens
            collector << "( "
          end

          collector =   case o.left
                        when Arel::Nodes::Union
                          visit_Arel_Nodes_Union o.left, collector, true
                        else
                          visit o.left, collector
          end

          collector << " UNION "

          collector =    case o.right
                         when Arel::Nodes::Union
                           visit_Arel_Nodes_Union o.right, collector, true
                         else
                           visit o.right, collector
          end

          if suppress_parens
            collector
          else
            collector << " )"
          end
        end

        def visit_Arel_Nodes_Bin(o, collector)
          collector << "BINARY "
          visit o.expr, collector
        end

        def visit_Arel_Nodes_UnqualifiedColumn(o, collector)
          visit o.expr, collector
        end

        ###
        # :'(
        # http://dev.mysql.com/doc/refman/5.0/en/select.html#id3482214
        def visit_Arel_Nodes_SelectStatement(o, collector)
          if o.offset && !o.limit
            o.limit = Arel::Nodes::Limit.new(18446744073709551615)
          end
          super
        end

        def visit_Arel_Nodes_SelectCore(o, collector)
          o.froms ||= Arel.sql("DUAL")
          super
        end

        def visit_Arel_Nodes_Concat(o, collector)
          collector << " CONCAT("
          visit o.left, collector
          collector << ", "
          visit o.right, collector
          collector << ") "
          collector
        end

        def build_subselect(key, o)
          subselect = super

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

          Nodes::SelectStatement.new.tap do |stmt|
            core = stmt.cores.last
            core.froms = Nodes::Grouping.new(subselect).as("__active_record_temp")
            core.projections = [Arel.sql(quote_column_name(key.name))]
          end
        end

        def collect_where_for(o, collector)
          return super if o.offset

          unless o.wheres.empty?
            collector << " WHERE "
            collector = inject_join o.wheres, collector, " AND "
          end

          unless o.orders.empty?
            collector << " ORDER BY "
            collector = inject_join o.orders, collector, ", "
          end

          maybe_visit o.limit, collector
        end
    end
  end
end