SQL join

Joinは時間がかかる。3.3ms↓
@fetch_symbols = Tick.all(:select => "name", :joins => :ticker_symbol).map { |u| u[:name]}.uniq

0.1+0.2+0.1ms = 0.4ms↓
m = Market[@market_config["market"]]
@fetch_symbols = TickerSymbol.find(m.ticks.map(&:ticker_symbol_id)).map(&:name)